Itachi Uchiha

Itachi Uchiha was an ANBU Captain and a prodigy from Konohagakure's famed Uchiha clan. He had joined the criminal organisation Akatsuki to serve as a double-spy, to later become an S-rank missing-nin as he participated in murder of his entire clan on orders from higher-ups, in what would become known as the Uchiha clan massacre, defecting from the village subsequently.

History
Itachi was born into the Uchiha clan as the eldest son of Mikotoand Fugaku Uchiha, and was praised by all as the best of his generation, and a genius above all others.Even by the standards of the battle-adept Uchiha clan, Itachi's prowess far outshone their own.However, few could understand him.When he was only four, Itachi had already witnessed countless lives lost due to the Third Shinobi World War, which emotionally traumatised him and consequently turned him into a pacifist.Itachi spent much of his time researching the history of the village from the writings their ancestors left behind. During the Nine-Tails' attack on Konoha, Itachi was left alone to take care of his infant brotherSasuke and promised to protect him no matter what.In the anime, it was shown that during their childhood, Itachi made a game of collecting paw prints of cats with his brother. The last paw print to be collected was Nekomata's, who Itachi had defeated and asked him to fight Sasuke with all his might when Sasuke got older. At age 7, Itachi graduated from the Academy at the top of his class after only one year,mastered the Sharingan at age 8,passed the Chūnin Exams at age 10, enrolled in ANBU half a year laterand became captain by 13.At some point in time in their childhood, Sasuke helped Itachi on one of his missions to capture a giant boar. Itachi told Sasuke to avoid his vital points. He then threw kunai with explosive tags around the boar, to confuse it and to give Sasuke an opportunity to shoot the boar. Sasuke, however, missed completely. After Sasuke apologised, Itachi told him he needs to train more.Itachi was praised highly by Fugaku, his father, who spent most of his time grooming Itachi to inherit the title of leader of the Uchiha, and hence inadvertently neglected his younger son. However, during this time Itachi showed great affection towards his little brother and even encouraged his father to come to the Academy enrolment ceremony for Sasuke, something their father had otherwise forgotten, caught up an important mission that would establish Itachi a place in the ANBU ranks. When the Uchiha clan began planning to overthrow Konoha, Itachi, as an ANBU, was tasked with spying on the village. Knowing that a coup d'état would only escalate to the beginning of another ninja-world war, Itachi began spying on the Uchiha instead, passing on information to the Third Hokage and Konoha elders. Though the Third Hokage ultimately decided to reason with the Uchiha in order to dissuade them from their actions, Danzō Shimura met secretly with Itachi Uchiha and inveigled him into choosing the lives of his clansmen or that of his little brother.Itachi eventually discovered the existence of Tobi — under the guise of a vengeful Madara Uchiha— who was attempting to rekindle the flames of war in Konoha. In return for not attacking Konoha, Itachi offered to help him claim vengeance against the Uchiha for turning their backs on him decades earlier to which Tobi agreed. Itachi joined Akatsuki, but did in fact in order to keep an eye on the organisation. During his time in Akatsuki, Orochimaru tried to steal his body to gain the Sharingan, but Itachi trapped him in a genjutsu and severed his left hand.Itachi was further partnered with Kisame Hoshigaki, who initially tried to intimidate him.However, they eventually became good partners. During this time he began to act strangely, not attending the clan meetings, speaking out against the clan, and becoming the prime suspect for the murder of his best friendShisui Uchiha, who was drowned in the Naka River. In reality, Shisui died after he entrusted his left eye to Itachi, the other having been taken by Danzō Shimura during Shisui's failed attempt to stop Danzō from carrying out his plan to commit genocide. Due to this the clan lost hope in Itachi, and his father began shifting his focus to Sasuke instead. Meanwhile, the Third's attempts to negotiate a bloodless end to hostilities between the two parties were proving ineffective, so against Hiruzen's wishes, Danzō Shimura and the Konoha Council ordered Itachi to wipe out the Uchiha clan. Before the fateful night arrived, Itachi with the help of Tobi under the guise of Madara Uchiha slaughtered his entire clan overnight.Despite this action, his parents stated that they were still proud of their eldest son, and requested that he took care of Sasuke. Itachi spared Sasuke because he loved his little brother, and as per the agreement between him and Danzō, did not want to take the life of the person most important to him. He lied to his brother, making himself out as a villain who had killed their innocent family only to test his capacity, and told Sasuke he was not even worth killing. Itachi also revealed to Sasuke the secret meeting place of the Uchiha, where Sasuke can learn the true history and purpose of the Sharingan. Itachi told him that in order to awaken the Mangekyō Sharingan, Sasuke had to kill the person closest to him, and that when they met again, they should have the same eyes. Sasuke managed to stand back up, awaken his Sharingan, and pursue Itachi. Upon reaching Itachi, he managed to knock off his forehead protector. Itachi shed a tear as he was picking up his forehead protector, then proceeded to incapacitate Sasuke, who awoke in the hospital, only remembering up to Itachi's speech. Hoping that his little brother would someday be powerful enough to kill him, Itachi left the village as a traitor.Knowing that Konoha would still want to eliminate Sasuke, Itachi pleaded with the Third Hokage to keep Sasuke safe and threatened Danzō not to harm Sasuke or else he would reveal everything he knew about Konoha's secrets to enemy nations.