Severus Snape/Synopsis

The story of Severus Snape from the Harry Potter franchise.

Early life
Severus Snape was born on January 9, 1960, on Spinner's End, a shabby suburb within a large Derbyshire County village in England called Cokeworth, where he spent much of his life under the stern eyes of his mother Eileen Prince-Snape, a former Gobstones (a game popular to young wizards and witches) champion, and mentally abused by his father Tobias Snape, a Muggle (non-magical) seasonal worker, both of whom were neglectful of his son and argued endlessly about where his future lied. This lack of care largely shaped Snape's bitter disposition and cruel behavior later in life, as well as his disdain of Muggles, and couldn't wait to to leave for the major wizarding school up in Scotland, called Hogwarts School of Witchcraft and Wizardry. He eventually came to see that Muggles could be gifted with magic too when he met Lily Evans, a young magically-gifted Muggle from a neighboring area with whom he fell in love with at first sight. After watching her for some time, Snape noticed her evident magical abilities after and began making friendly overtures by revealing that her strange powers were signs of witchcraft. The two treated each other distainfully at first, but Lily was intrigued by him and became his best friend. He spent hours describing the magical world around them to her, though the sight of them together and her older sister Petunia, whom Snape  developed a contempt towards after  she made disparaging comments about his clothes and residence. but may also be because she was a Muggle who had no understanding of magic and wanted nothing to do with it.

At the start of their first year at Hogwarts, Snape and Lily still made a close bond despite being in different school houses. While Lily was sorted in Gryffindor due to her Muggle-born status and courage, Snape ended up in Slytherin due to his resourcefulness with the Dark Arts and ambition from the abuse given by his father. While there, he made  good rapport   with Slytherin prefect  Lucius Malfoy  as the two grew to share their extremist ideals,  and became part of a small gang of Slytherins (consisting of Evan Rosier, Gaspar Avery, Adam Mulciber and Wilkes) which embraced dark magic and pure-blood supremacy, the views and qualities of which even Lily was offended by since it marked Muggle-borns, half-bloods, blood traitors and even half-breeds a disgrace to wizardkind. Snape nonetheless proved to be a talented student credited for knowing more spells and curses than anyone in seventh year (including his signature curse Sectumesmpra), most of which he invented and scribbled into his mother's old copy of Advance Potion-Making (which he signed with his self-used nickname, the "Half-Blood Prince") ''. ''but never missed an opportunity to cause them trouble even if they the teachers doubted they deserved such, including Hogwarts headmaster Albus Dumbledore.

Although starting to drift away from Lily, he considered many Gryffindors such as those she made friends with to be self-righteous and arrogant, with no regard for rules. This was evident due to a bitter and reciprocated hatred Snape harbored against a small gang of Gryffindors known as the Marauders (consisting of James Potter, Sirius Black, Peter Pettigrew and Remus Lupin), who were constantly at war with him throughout their school years. Immediately since meeting on the Hogwarts Express in their first year, Snape and Potter came to resent each other due to the latter's popularity and the former's interest in the Dark Arts, and their close love for Lily heightened the tension between the two. Further interactions between them made their rivalry tense and permanent, as Potter constantly bullied Snape with his own invented spells for his amusement. In retaliation, however, Snape occasionally followed the Marauders around, looking for reasons to get them expelled. At one point, he noticed that Lupin kept disappearing during the full moon and followed him into the tunnel under the Whomping Willow planted on the school grounds, having been tipped off by Black on getting past the tree's branch defenses. When Potter found out what happened, he went after Snape and pulled him back, but not before Snape glimpsed Lupin transforming into a werewolf in the supposedly-haunted Shrieking Shack at the other end of the tunnel. Dumbledore swore all three boys (Snape, Potter, Black and Pettigrew) to keep such discovery a secret, but Lupin's supposed true nature was clear to Snape, who in addition believed Potter's actions were self-serving to avoid expulsion.

Snape tried to run from the Marauders after finishing his homework under a tree on the Hogwarts grounds, but Potter hoisted him upside-down to reveal his underwear in front of many students. Lily came to Snape's defence, but this only made things worse: in a subsequent lashing out at Potter in an attempt to recover his lost dignity, Snape inadvertently called Lily a "Mudblood" (the foulest name to call a Muggle-born). Lily refused to forgive him for it, even after his repeated apologies. Hoping to get payback from the Marauders, By their seventh year, Potter grew out of his immaturity and arrogance to the point that Lily agreed to start dating him, even though he never grew out of his hatred for Snape. Lily ended up marrying Potter, which only strengthened Snape's bitterness towards him.

Following his graduation from Hogwarts, Snape joined his old Slytherin gang within the ranks of the Death Eaters, an army of supremacistic witches and wizards led by the psychopathic dark wizard Lord Voldemort, who aimed take over the wizarding world and shape it in his supremacist views through his tyrannical rise to power. Voldemort was a difficult taskmaster of limited patience and did not take kindly to failure from his followers, but Snape had little difficulty in gaining the Dark Lord’s favor. Nonetheless, he was counted among one of the Voldemort’s most trusted servants and went above average intelligence and ability, both of which he turned to crimes like coercion, torture and murder. He fought at his master's side in a few battles during the war, and was presumably involved in the deaths and disappearances of several members of the Order of the Phoenix, around whom opposition to Voldemort was always rallied. Due to his attachment to Hogwarts, Snape was ideally positioned to gain insight into Dumbledore's resources and yet-to-be initiated plans aimed to crush the Dark Rebellion, all of which were valuable information he relayed to the Death Eaters. The sneering wizard soon thought he saw a chance to win Voldemort's full trust when picking up tips for a job at the school itself in the nearby village of Hogsmeade. While stopping at the Hog's Head pub, he eavesdropped on Dumbledore's interview with new Divination professor Sybil Trelanwey at the restaurant inn, during which Trelanwey prophesied a child born at the end of July would be marked as Voldemort's equal and cause the dark wizard's destruction (which prompted Dumbledore to hire her, partly for her own safety). Snape did not hear the entire prophecy, however, as the Dumbledore's brother Anberforth, who worked as the restaurant's barman, caught him and threw him out.

Although his information on the prophecy was incomplete, Snape reported to Voldemort what he heard. At that time, it was unclear who was meant by the prophecy, but two boys of prominent wizarding families were born that year at the end of July: Lily's son Harry Potter and his future Hogwarts classmate Neville Longbottom. Snape suffered terrible remorse when Voldemort decided that Harry Potter was the subject of the prophecy, and that Lily and her husband were marked for death along with their son as a result of his own actions. He begged Voldemort to spare her in exchange for the lives of her husband and son using his skills in Occlumency (the art of magically shielding a witch or wizard's own mind against external penetration) against his master's Legilimency in order to avoid exposing his true feelings for Lily. but knowing that he couldn't leave Lily's safety at the hands of someone who could turn his back on his word since she would probably defend her child to the last breath, he approached Dumbledore and asked him to save her by hiding her along with her husband and son if necessary. Dumbledore agreed, but insisted that Snape served him in the order of the phoenix and masquerade as a spy among the Death Eaters.

Dumbledore kept his word for Snape by hiding the Potters from Voldemort via a Fidelius Charm over their family home in the wizard-famous village of Godric's Hollow, offering himself as the family Secret-Keeper. The Potters turned the offer down, insisting that a godfather of Harry's like Sirius Black was brave enough to die while holding the position. At Black's suggestions, however, they decided to use him as a decoy while Peter Pettigrew became Secret-Keeper, but Pettigrew later turned out to be spy for the Death Eaters, tipping Voldemort off on their whereabouts and using Snape and the rest of the wizarding world's belief that Black actually agreed to take the job to frame him for the betrayal. Because of this, Voldemort found the Potters anyway, but the loving sacrifice Lily made in order for Harry to live caused the dark wizard's Killing Curse for the boy to rebound on Voldemort himself, destroying his body but not his soul (which was split into Horcruxes to make him immortal), thus leaving his army shocked and distraught as well as making Harry famous for being the first to survive one of the killing Curse. Snape was devastated and distraught to the point of wishing himself dead, but Dumbledore urged him to ensure Harry's safety out of respect for Lily's memory; Snape was initially hesitant, for he (like many other Death Eaters) believed that their master was gone for good and the danger was averted. However, he knew deep down that the Dark Lord wasn't truly dead yet and would return someday as Dumbledore reminded him, and everyone (particularly the boy) would be in danger when that happened, So Snape spent the rest of his life protecting Harry Potter, who was often said to strongly resemble his father. Distrusted for his past as a Death Eater by those on Dumbledore's side, and hated by other Death Eaters for living as Dumbledore's stooge, he continued living on to complete Dumbledore's plan.

When Snape began his teaching career at Hogwarts, he initially applied for the position of Defense Against the Dark Arts professor but was rejected multiple times. Many students were under the impression that this was because Dumbledore feared Snape might return to his old ways if allowed to teach his favorite subject, but in reality it was because he was aware by that point that the job was jinxed by Voldemort. Knowing that this jinx restricted every professor of the subject from lasting longer than a year, Dumbledore instead appointed Snape as Potions professor and head of Slytherin following the resignation of veteran Potions professor Horace Slughorn. Though it seemed rather uncommon for someone so young to be named Head of any house at Hogwarts, it was possible that Snape was the only Slytherin teacher left at the school, or that he was placed there to keep a watchful eye on young Slytherins frequently accused of (but not without reason) joining the Death Eaters. Following Voldemort's fall, Snape never attempted to find him, and he used Dumbledore's protection to avoid serving time in the wizard prison. Eventually, he accepted this thought as unavoidable. In the meantime, he focused on his teaching duties at Hogwarts. As a professor, Snape was a stickler for discipline, with little patience for foolishness, yet extremely effective in his job and well respected by the other professors. His deep understanding of potion brewing transformed the knowledge of potions from mere chemistry to an art. This was unfortunate for his classes. He accepted students into his N.E.W.T. classes only if they had achieved an 'Outstanding' mark at their O.W.L. examination, as he felt that anyone with a lower mark than that would lack both the necessary passion for and devotion to the complex of subjects that would follow in the last two years of school. Though strict, Snape had a certain level of bias for Slytherins, giving them undeserved rights over the others, while looking down on the other students somewhat unfairly.

Harry Potter and the Philosopher's Stone
Ten years later, when Nicolas Flamel (who was a friend of Dumbledore's) had the Philosopher's Stone that was keeping him alive moved from his safe in Gringotts Wizarding Bank to Hogwarts for safe keeping, Snape contributed to the defenses set up around the magical artifact by adding in a Potions Riddle as the obstacle with a table holding seven unlabeled bottles of differing shapes and sizes. At the same time, Harry Potter arrived for his first year at the school, and the two of them detested each other almost immediately since the boy's resemblance to his father and his acquired 'celebrity' status brought the worst out of Snape from their very first Potions lesson, in which he made a frequent snide and disparaging remarks at Harry's expense. Although Snape had pledged an oath to Dumbledore that he would protect Harry, such oath did not stand in the way of Snape's bias to Slytherin, nor did it mean Harry was to get any special treatment in academics.

Because he suspected that the new Defense Against the Dark Arts professor Quirinus Quirrell was trying to help Voldemort steal the Philosopher's Stone, Snape promised Dumbledore to keep a close eye on him all year, and did everything he could to prevent the theft. The turbaned professor first made his move in carrying out the Dark Lord's scheme by allowing a mountain troll enter Hogwarts during the Halloween celebrations as a diversion. Snape took this chance to stop him from sneaking to the restricted third floor corridor where the Stone was being hidden in the midst of the chaotic event, only to get bitten in the leg by the corridor's three-headed watchdog Fluffy. Later in the year, when Quirrell made his first attempt on Harry's life by jinxing the boy's new broomstick during his first Quidditch match, Snape interfered again by performing a counter-curse to prevent Harry himself from being hurled off. Unfortunately, Harry's his best friends Ron Weasley and Hermione Granger observed the crowd through binoculars to figure out who was performing the jinx and caught Snape discreetly uttering the counter-curse incantation, but erroneously thought he was performing the actual curse. So Hernmione ran to his stand and set fire to his robes in order to distract him and make him stop, yet luckily for Snape, she accidentally knocked Quirrell over during her hurry back to the Gryffindor stands, causing him to break the eye contact necessary for performing his spell correctly. For the next match, Snape insisted on refereeing to ensure that Quirrel's stunts against Harry never happened again, but this did not come across well to the other teachers, who believed he was just trying to injure the Gryffindor Quidditch team's chances of winning. Harry, on the other hand, suspected that this was another attempt on his life and won the game quickly by catching the Golden Snitch within five minutes of it starting, whereas Snape was knocked out cold by a Bludger hit toward him by Ron's older brothers Fred and George.

Later that night following the match, Snape intensely confronted Quirrell in the Forbidden Forest, demanding to know why he was after the Philosopher's Stone. Unknown to them both, Harry was watching the entire argument from the treetops, having followed the Potions professor into the forest on his broomstick after passing him at the school Quidditch shed. But because the boy suspected Snape of plotting to steal the stone and of attempting to kill him, it seemed to him that the Potions professor was trying to intimidate Quirrel into handing over information regarding the artifact. So he, Ron and Hermione unjustly tried to be supportive and encouraging to Quirrell whenever possible by telling people off for laughing at his stutter, smiling at him encouragingly whenever they passed him or arguing with Snape. The trio were eventually told by the half-giant Hogwarts gamekeeper Rubeus Hagrid how the snobbish professor helped guard the stone, but were still unconvinced of Snape's mysterious motives until learning that the half-giant won his new pet Norweigan Ridgeback Norbert (who had to let go when her existence started became known) from a card game against a hooded stranger who was then told in return how to get past Fluffy. Snape, on the other hand, grew very concerned of the three students when they brushed by in the school hall to inform Dumbledore of the situation, but learned that the old wizard departed for London to respond to an urgent (but fake) owl message from the Ministry of Magic actually sent to him by Quirrell. Knowing that Lily would not allow her son to be hanging around with his friends looking as though they were up to something, the stern teacher reminded them that Gryffindor could not afford to lose more house points. Harry deduced that his Potions professor would try stealing the Stone at night with everyone asleep, so they headed out undetected to retrieve the legendary artifact themselves.

By successfully making it into the third-floor corridor, the trio put Fluffy to sleep using a flute Hagrid gave Harry for Christmas, then ventured through the trapdoor underneath him and passed through five of the defenses which the other professors set up around it, the fourth of which Ron got injured from and had to be left behind. The defense with the Potions Riddle set up by Snape himself came up as the sixth and last obstacle, where they had to figure out the potion line-up to find the potion which would make its drinker safely traverse the black flame blocking their exit. Hermione immediately figured out the line-up and drank the bottle containing a potion that allowed passage back through the purple flames blocking the entrance, so that she could go back and help Ron and send an owl to summon Dumbledore, leaving Harry with the option of drinking the potion meant for the black flames and move ahead. It was there in the last chamber behind those flames which supposedly contained the Stone that Quirrell was finally revealed to be the real mastermind behind the plot to steal it for Voldemort and the attempts on the young Potter's life. The turbaned professor mentioned that both Snape and James Potter detested each other while at school, and Voldemort (who was seen sharing Quirrel's body) had him strangle the boy to the ground when they both saw that the fabled Mirror of Erised in front of them gave the Stone to Harry, whose wish was to find it with no intention of using it or having it used. Luckily for the protective barrier around Harry from his mother's sacrifice, however, Quirrell was unable to touch him without casing harm to himself, and disintegrated from the physical contact.

Harry began to doubt whether or not Snape would have wanted any harm to come to him during his conversation with Dumbledore in the school hospital wing, but Dumbledore suggested that because Harry's father saved Snape's life when they were both students, Snape felt responsible for Harry in return. Because this was not the full story, he retained feelings of suspicion and resentment towards Snape, and their relationship remained tense. Snape's behavior and attitude towards Harry, on the other hand, also remained unchanged.

Harry Potter and the Chamber of Secrets
When Snape learned from the Daily Prophet of Muggles sighting Harry and Ron travelling to Hogwarts in a flying car instead of on the Hogwarts Express at the start of their second year, he threatened to have them expelled, but Dumbledore and his deputy headmistress, Transfiguration professor Minerva McGonagall, stepped in and made sure it did not happen by instead giving a warning and separate detentions. He eventually retaliated to this by allowing the Slytherin Quidditch team to unfairly usurp the Quidditch pitch during the Gryffindor team's practice time, all in order for them to train their new Seeker: Lucius Malfoy's son Draco, who was Harry's rival since the previous year. After the Halloween celebrations, when the entire school found Mrs. Norris (the pet cat of school caretaker Argus Filch) hanging by the tail from a torch all petrified with a message announcing the legendary Chamber of Secrets' re-opening written in blood on the wall above her and Harry, Ron and Hermione already at the scene, Snape tried to help Filch get the trio in trouble for it. However, Dumbledore implied that it was powerful dark magic that no second year student could perform, and decided that the Mandrakes of Herbology professor Panoma Sprout should be used, once they were mature enough, to create a draught capable of reviving the cat.

The arrogant Potions professor continued to blame Harry for whatever incident that occurred throughout the school year. The first of which was when the boy managed to successfully create a spectacle of a diversion in Potions class long enough for Hermione to smuggle Polyjuice Potion ingredients from Snape's personal cabinets. When Snape helped celebrity author and new Defense Against the Dark Arts professor Gilderoy Lockhart oversee Hogwarts' short-lived Dueling Club, both professors opened the activity with a demonstration of formal duelling, including the accepted combative position. Snape, however, was rather crude with his greeting and demonstrated to the students (including Harry) an Expelliarmus charm so powerful that it sent Lochkhart flying into a nearby wall. Presumably deciding that the Potions teacher was far too skillful for him, Lockhart barely covered his own ineptitude by lying that allowed Snape to disarm him just to make a fool of himself. He then let the students break off into pairs to practice disarming, but as the room dissolved into chaos, Snape had to break them up with a Finite Incantatum charm and suggested that teaching them how to block unfriendly spells, to which Lockhart agreed despite having no idea how to do it himself. The two rival teachers had Harry and Draco paired together on their own, with Snape giving Draco the idea to frighten Harry out of his wits by conjuring a large black snake with a Snake Summons Spell. When Lockhart's failed attempt to get rid of the snake instead lifted it a few feet into the air and attack Muggle-born Hufflepuff student Justin Finch-Fletchley in a fit of rage when it landed, Harry luckily ordered the reptile to stop in Parseltongue (a language that mostly dark wizards use to communicate with snakes), unaware of what he was doing nor how his classmates were reacting to it. This gave Snape the opportunity to vanish the snake, despite how horrified he was to discover this secret about his childhood love interest's son, and end the meeting quickly.

For a while, most of the school, including Snape, assumed that Harry must be the heir of Hogwarts founder Salazar Slytherin capable of opening the Chamber of Secrets and releasing the Basilisk living inside. Dumbledore, however, did not believe that such a gifted boy could possibly been behind the attacks on Muggle-born students that occurred since Mrs. Norris' attack, yet it remained unclear if Snape ever knew that Harry would try to prove his innocence by disguising himself and Ron as Draco's cronies Vincent Crabbe and Gregory Goyle, to get information about the last time the chamber was opened from the young Malfoy himself. The potions master luckily payed little attention to the boy and faced a bigger problem that he had for himself that initially involved Lockhart, who embarrassed him during the rest of the school year to the point during the Valentine's Day celebrations in which the celebrity author made insensitive comments about Entrancing Enchantments and love potions towards Snape and Flitwick. This made Flitwick bury his face in his hands in embarrassment, and Snape looked as though he would force the first person who dared to ask him for a love potion to eat poison. The impact that the Basilisk had on Hogwarts started worsening with the attacks on three more Muggle-born students, including Hermione. This rise of terror eventually got Hagrid arrested by the Minister of Magic Cornelius Fudge since he was wrongly accused of opening the Chamber last time, and Dumbledore getting dismissed from his position of headmaster by Lucius Malfoy himself, who was now working as one of the twelve school governors.

The attacks soon stopped after the petrification of Hermione and Ravenclaw prefect Penelope Clearwater. But when the Basilisk's supposed abduction of Ron's younger sister Ginny caught the attention of the Hogwarts staff, Snape convinced them to task Lockhart (who had recently claimed to have known the location of the Chamber's entrance all along) with fighting the Basilisk and saving its hostage so that the snobbish professor himself could obtain the actual information on the Chamber's entrance from Harry (if he knew that Harry had solved the mystery behind the Chamber itself) and wrongly expose her as the culprit behind the attacks and get her expelled for Harry's safety. Unbeknownst to anyone,

Harry Potter and the Prisoner of Azkaban
In Harry Potter and the Prisoner of Azkaban, Snape demonstrates his expertise with potions by brewing the complex Wolfsbane potion for the new Defence Against the Dark Arts professor, Remus Lupin. Throughout the third book, Snape suspects that Lupin may be helping Sirius Black enter Hogwarts castle; Sirius had been convicted (wrongly, as it is later revealed) of murdering innocent bystanders and betraying the Potter family's hiding place to Voldemort. This suspicion stems from Lupin's friendship with Sirius and Harry's father, James, while they were all at Hogwarts as students. Near the climax of the book, Snape attempts to apprehend Black, but Black escapes with Harry's aid. Snape informs Dumbledore of this circumstance, and when Harry and Lupin are not punished, Snape retaliates by revealing to the entire school that Lupin is a werewolf, forcing the latter to resign his post.

Harry Potter and the Goblet of Fire
Snape's role in the fourth novel, Harry Potter and the Goblet of Fire, is not substantially different from that of the previous three books. He is apoplectic when Harry is unexpectedly entered into the Triwizard Tournament. Later Harry accidentally falls into Dumbledore's Pensieve and views memories of several Death Eater trials from years before. At one point, Snape is named as a Death Eater by Igor Karkaroff, but Dumbledore comes to Snape's defense, claiming that although Snape had indeed been a Death Eater, he changed sides before Voldemort's downfall and turned spy against him. Later, Dumbledore assures Harry that Snape's reformation is genuine, though he refuses to tell Harry how he knows this, saying the information "is a matter between Professor Snape and myself".

At the end of the book, Dumbledore attempts to convince a disbelieving Minister for Magic, Cornelius Fudge, that Voldemort has returned. As proof, Snape willingly shows Fudge the restored Dark Mark on his arm. He is subsequently sent on a secret mission by Dumbledore. This mission, as had been implied in Harry Potter and the Order of the Phoenix and revealed in Harry Potter and the Half-Blood Prince, was to rejoin the Death Eaters and spy on Voldemort as a re-doubled agent, while pretending to spy on Dumbledore on behalf of Voldemort.

Harry Potter and the Order of the Phoenix
In the fifth novel, Harry Potter and the Order of the Phoenix, Snape returns to a more prominent role. With Voldemort having returned to a fully corporeal body, Snape continues working as a re-doubled agent for Dumbledore. He is seen prior to the start of school at Number 12, Grimmauld Place giving reports to the Order of the Phoenix. He has a very strained relationship with Sirius, who owns Grimmauld Place and must remain there in hiding. The two trade frequent snide remarks and at one point almost begin a duel. Snape taunts Sirius about the latter's not being able to take an active role in the Order's missions because of his fugitive status. Harry feels later that this taunting contributed to Sirius's willingness to take unsafe risks. Back at school, Snape's allegiance to the Order has no effect on his dislike for Harry.

Later in the book, Dumbledore has Snape teach Harry Occlumency, the protection of the mind from outside intrusion or influence. The sessions are made difficult by their mutual hostility and end prematurely when Harry uses Dumbledore's Pensieve to view one of Snape's worst childhood memories without the latter's permission. He sees the memory of Snape being bullied by James and Sirius, and of calling Harry's mother, Lily Evans, a Mudblood (a highly offensive term). Only in the final book is it revealed that, prior to this confrontation, Snape and Lily had been close friends.

Towards the end of the novel, Dolores Umbridge –the school's politically-appointed headmaster–captures Harry and interrogates him about Dumbledore's whereabouts. She sends for Snape to provide a truth serum to force Harry to reveal any information he may be hiding. Snape claims that his supplies of Veritaserum were exhausted earlier, when she had attempted to use the drug surreptitiously to force information from Harry. Snape withholds further assistance. It is later revealed that Snape had in fact supplied Umbridge with fake Veritaserum on the prior attempt. Snape then carries Harry's cryptic warning about Sirius' capture to the other Order members, allowing them to come to the rescue in the Department of Mysteries. Harry still holds Snape partly responsible for Sirius's death, believing Snape's goading spurred Sirius into joining the battle.

Double-Agent for both sides
Snape returns as the eponymous titular character and the main antagonist in the sixth novel, Harry Potter and the Half-Blood Prince. In the second chapter of Harry Potter and the Half-Blood Prince, Bellatrix Lestrange and Narcissa Malfoy visit Snape at his home in Spinner's End. Narcissa's son Draco has been given a difficult task by Voldemort, and Narcissa swears Snape to an Unbreakable Vow that he will protect Draco, help him complete Voldemort's task, and finish the task himself if Draco fails. When questioned by Bellatrix about his loyalties, Snape says he has been working for Voldemort ever since Voldemort's return, and explains his actions in the previous books in that light. He points out that gaining Dumbledore's trust and protection has kept him out of Azkaban and free to operate on Voldemort's behalf.

Harry's discovery of the Half-Blood Prince's Potions textbook
At the start-of-term feast at Hogwarts, Dumbledore announces Snape as the new Defence Against the Dark Arts professor. Horace Slughorn, a retired Hogwarts teacher, replaces Snape as Potions Master. With Snape no longer teaching Potions, Harry enrolls in Slughorn's class and is lent an old textbook until his new one arrives. Harry finds marginalia, including a variety of hexes and jinxes seemingly invented by an unknown student, and substantial improvements to the book's standard potion-making instructions. The text is inscribed as being "the Property of the Half-Blood Prince". The notes greatly bolster Harry's performance in Potions, so much so that he impresses Slughorn. Snape, who maintains that he "never had the impression that [he] had been able to teach Potter anything at all", is suspicious of Harry's newfound Potions success.

Later, during a fight with Draco, Harry casts one of the Prince's spells marked "For Enemies," and is horrified by the devastating wounds it inflicts to Draco's face and chest. Snape rushes to the scene and heals Draco, then interrogates Harry regarding the spell, using Legilimency to extract the source of Harry's knowledge (the Potions textbook) from Harry's mind. When Snape insists that Harry show him his Potions textbook, Harry hides the Prince's book and gives him Ron Weasley's book instead. As punishment for the attack and knowing Harry is lying about the textbook, Snape assigns Harry detention during the final Quidditch match of the year.

Before leaving Hogwarts to accompany Dumbledore in locating another horcrux –part of Voldemort's soul– Harry discovers from Professor Trelawney that it was Snape who overheard the prophecy and told it to Voldemort, resulting in Voldemort hunting down Harry and his parents. Despite this and Harry's angry questions, Dumbledore avers his trust in Snape. Returning to Hogwarts after retrieving Voldemort's Horcrux, Harry and Dumbledore alight atop the school's astronomy tower. Gravely weakened by the horcrux's protective potion, Dumbledore tells Harry he must fetch Snape, but before Harry can leave, Draco suddenly arrives, intending to carry out Voldemort's order to assassinate Dumbledore, closely followed by other Death Eaters (followers of Voldemort), and Snape.

Killing Dumbledore
Snape interrupts the planned murder, by killing the headmaster himself, so that Draco didn't have to. He falls off the tower (often compared to when Scar dropped Mufasa to his death in The Lion King). Harry, who is paralyzed under his invisibility cloak by Dumbledore for his own protection, witnesses the murder, and is released upon Dumbledore's death. Enraged, he pursues Snape, Draco, and the Death Eaters as they flee the castle.

After fighting through several lethal Death Eaters, Harry confronts Snape by Hagrid's Hut. The two of them engage in a deadly duel, which increasingly becomes hopelessly one-sided in Snape's favour. Snape easily overpowers Harry by reading his mind and predicting his opponent's moves, using them against him - he only directly struck out once, at the climax of the duel, after revealing himself as the eponymous "Half-Blood Prince" (being the half-blood son of Muggle Tobias Snape and pure-blood Eileen Prince).

After incapacitating Harry, Snape passes through the school gates and Disapparates with Draco in tow at the book's end. The full relationship between Dumbledore and Snape and the reason for Snape's actions remain unknown until the final book. In an interview, Rowling mentioned that at this point in the series, the Harry–Snape relationship has become "as personal, if not more so, than Harry–Voldemort."

Headmaster of Hogwarts
In Harry Potter and the Deathly Hallows, Voldemort and his Death Eaters have tightened their grip on the wizarding world. Snape is named Headmaster of Hogwarts, while Death Eaters Alecto and Amycus Carrow are appointed as Hogwarts staff. The novel focuses largely on Harry and his friends, and events outside the school; therefore Snape plays a limited role at the start. In the course of the book, Harry and Ron are led to find the Sword of Godric Gryffindor by a Patronus taking the form of a doe. (Towards the end of the book, Harry learns that this was Snape's Patronus, taking the same shape as Harry's mother Lily's Patronus, a visible sign of his lifelong love for Harry's mother, and that Dumbledore had asked Snape to ensure that Harry gained possession of the sword. The novel also reveals that Snape had covertly used his position as Headmaster to protect the students and to contain the Carrows.)

Betraying Voldemort and Death
Towards the end of the school year, Professors McGonagall, Flitwick, and Sprout force Snape to flee the school. After an intense duel with McGonagall, Snape retreats to join the Death Eaters. He fights in the Battle of Hogwarts, but his full role remains unknown, until Voldemort summons Snape to meet in the Shrieking Shack. Voldemort explains to Snape that he believes that he has become the master of the Elder Wand by killing Dumbledore and that Snape's death will make him the master of the Wand. Snape tries to explain but Voldemort kills Snape by having his pet snake Nagini bite him through the neck. The dying Snape releases a cloud of memories and tells Harry, who has watched the entire scene from a hidden spot, to take and view them. With his last breaths, Snape tells Harry that he has his mother's eyes and then dies.

Extracted memories viewed by Harry
From these memories, Harry sees Snape's childhood and learns his true loyalties. In this vision, Harry learns that Snape befriended Lily as a child when they lived near each other. Upon their arrival at Hogwarts, the Sorting Hat placed Snape and Lily into Slytherin and Gryffindor Houses, respectively. They remained friends for the next few years until they were driven apart by Snape's interest in the Dark Arts; the friendship finally ended following the bullying episode that Harry had briefly seen in the fifth book, in which Snape calls Lily "Mudblood". Despite this separation and Snape's enduring animosity toward Lily's eventual husband James Potter, Snape continued to love Lily for the rest of his life.

The memories also show that as a Death Eater, Snape had revealed to Voldemort a prophecy made by Sybill Trelawney, causing Voldemort to attempt to prevent it by killing Harry and his parents. Snape, who had not realized until too late that the prophecy was referring to Lily and her family, asked Voldemort to spare Lily. Still in terror for her life, he also approached Dumbledore, admitted his actions, and begged him to protect the Potters. Dumbledore chided him for thinking only of himself and not of Lily's husband and child, but agreed and ensured that they were placed under the Fidelius Charm. In return, Snape secretly allied himself with Dumbledore and the Order of the Phoenix as a re-doubled agent against Voldemort, using his powers of Occlumency to hide his betrayal from Voldemort. However, Snape demanded of Dumbledore that his love for Lily (his reason for switching sides) be kept a secret, especially from Harry, because of the deep animosity he felt towards Harry's father and his mixed feelings towards Harry (who reminded him of both his love for Lily Potter and her death, and his animosity towards James Potter). Dumbledore agreed and kept the secret throughout his life, although questioning Snape's request to "never reveal the best of you". Even with his efforts to protect her, Snape felt responsible for Lily's death at Voldemort's hands. Snape's memories then reveal that Dumbledore had impetuously tried to use the Gaunt ring which had been cursed by Voldemort, and had been suffering from a powerful curse. Snape's knowledge of the Dark Arts enabled him to slow the spread of the curse from Dumbledore's hand through his body, but he would have died within a year. Dumbledore, aware that Voldemort had ordered Draco to kill him, had asked Snape to kill him instead as a way of sparing the boy's soul and of preventing his own otherwise slow, painful death. Although Snape was reluctant, even asking about the impact of such an action on his own soul, Dumbledore implied that this kind of coup de grâce would not damage a human's soul in the same way murder would. Snape agreed to do as the Headmaster requested. Snape's memories also provide Harry with the information he needs to ensure Voldemort's final defeat, in the form of conversations Snape had with Dumbledore.

Epilogue
In the epilogue to Deathly Hallows, set nineteen years after Harry defeats Voldemort, Harry has named his second-born son Albus Severus, after Albus Dumbledore and Severus Snape. As Albus is about to enter his first year at Hogwarts, he expresses concern that he will be sorted into Slytherin. Harry tells his son, "you were named for two headmasters of Hogwarts. One of them (Snape) was a Slytherin and he was probably the bravest man I ever knew."

Rowling interview about Snape
Rowling noted in an interview that because Snape abandoned his post before dying or officially retiring, a portrait of him does not immediately appear in the Headmaster's office following his death. She adds, however, that she would like to think Harry made Snape's true loyalty and heroism known in the Wizarding world, and that he lobbied to ensure that a portrait be installed in the office. In a separate interview, Rowling discussed Snape's back story, saying she had planned it ever since she wrote the first book because the whole series is built around it and she considers him one of the most important characters of the seventh book.