Adam Millagan is minor character in season 5 and supporting character in season 15. He is the younger half-brother of Sam and Dean Winchester the son of John Winchester and Kate Millagan, and the step-son of Mary Winchester in the CW's hit-tv series Supernatural. He was killed by a Ghoul but was resurrected by angels to serve as a vessel for Michael but this turned out to be a ploy to convince Dean to concede to saying "yes" to the archangel. He was played by Jake Abel.
Adam is described as the polar opposite of Sam and Dean Winchester, As comparing him to Dean is that he loves liquor, music, women and hamburgers along with starting fights with older people.
Comparing Adam to Sam is much more different but the two are similar in certain topics such as having a complicated relationship with their father and questioning Dean's actions.
While he was slow to connect with his half-brothers even telling them they are not his family, he came to trust them to a certain extent when he was skeptical of Zachariah's intentions. He was also touched when both came to rescue him after he saw they were right about Zachariah and called him family.
Adam Millagan was the estranged son of John Winchester who met Adam's mother Kate when he was injured and being a nurse she tended to him. The two formed a relationship before John left town unaware that she was pregnant with their son.
When Adam was twelve he begged his mother to contact John, to which she did. After learning of Adam, John headed back to Kate and met his son who he decided to connect with. It was speculated by Dean that John saw Adam as a chance to raise a son in a normal way instead putting him in the dangerous path of a hunter. Also, the time John found about Adam goes along with the time frame Sam decided to attend college, leaving him and his older brother Dean alone. This means he wanted Adam to fill in the role of the son who he can be fatherly to.
John would have many meetings with Adam in the future; taking him to baseball games, teaching him how to drive and giving him a beer on his fifteenth birthday. Despite John trying to be a father to him, Adam never saw him as such and only viewed his mother Kate Millagan as his family. Also, John never told Sam and Dean about Adam while Adam was never informed of John's previous life or his other sons.
However, being John Winchester's son brought about suffering to both Adam and Kate that causes both to die at the hands of ghouls who wanting revenge on John. Adam was killed by the monsters with one of them taking on his form and the other taking his mother's form.
When this fake Adam first appeared in the series, he met Sam and Dean who were surprised to learn they had a half-brother. This Adam lured them to the house and tricked them in its plot to kill them as the ghouls were children of another ghoul John killed. Since John was already dead, his other children (Sam and Dean) had to pay the price of his sin, with the Kate ghoul confirming to a captured Sam that the real Adam was indeed the Winchesters' brother.
Sam and Dean killed the ghouls before finding the real Adam's body and giving it a hunter's funeral, out of respect for the brother they never knew.
Eventually in Season 5, the angels resurrected Adam from the dead as part of their "plan" to kill Lucifer. Adam is found by Castiel who takes him back to his brothers Sam and Dean. Adam then formally meets his siblings but he knew who they were as the angels warned him about them and how the angels needed him alive for their "Plan" to ignite the Apocalyspe and allow Michael (the Greatest and most powerful Archangel of all of God's Children) to possess him.
Adam insists that he complies as he'll see his mother again as he disagrees with their words that Michael is lying as he knows that the fight with Lucifer will possibly deep-fry the planet along with the angels. Adam is distant to Sam and Dean even stating they are not his family and he will see his mother again before they get him to at least give them time.
Adam later tries to sneak out but Sam finds him and they talk with Adam once again giving him the cold shoulder and for using their father as a trump card, before an exasperated Sam leaves telling Adam he'll fit right in with the family with his attitude. Zachariah later appears to Adam in a dream to get him to side with him but Adam shows he gained some form of faith in his brothers as he is distrustful of the latter's intentions. Zachariah uses Adam's mother as leverage causing him to leave with the angel.
While waiting on Michael, Adam dines on burgers which causes Zachariah to remark he shares the same tastes in food as Dean. Adam inquires as to where the Arch angel was before Zachariah reveals that everything was a lie to lure in Dean as he knew the Winchesters would come to save him. Realizing his brothers were right, Adam protests as Zachariah tells him he'll get his mother back but Adam doesn't believe it so Zachariah tortures him to silence him.
Adam lays on the ground in pain when Dean comes to rescue him as Adam was very shocked that he came despite his treatment. Dean replies by calling him family while Adam tries to warn of the trap but it is too late as Zachariah appeared and even subdued Sam after he sneaks up on him. Zachariah tortures both Sam and Adam, as a horrified Dean watches as both his brothers are forced to cough up blood. Dean reluctantly accepted Zachariah's demand to submit to Michael as Zachariah summoned but this gave Dean the chance to kill the cruel angel with a hidden angel blade. As Michael arrives Dean and Sam escape, and despite Dean's vain attempts to save Adam he ends up being trapped in the building and taken away by Michael.
Unable to get his hands on Dean, Michael ends up getting Adam to say yes to being his vessel, which ends up with Adam being possessed. In Adam's body, Michael meets with Lucifer (who is now using Sam as a vessel) in order to fight him, but they are interrupted by the arrival of Dean who is there to try and get through to Sam and make him take his body back from Lucifer. During this encounter Dean aplogises to Adam for what he is about to do, which leads to Michael mockingly telling him that Adam isn't aware of what is going on at this moment in time. Castiel uses holy fire to temporarily banish Michael away, just in time for Dean to get through to Sam. Sam retakes his body and struggles to keep Lucifer in control, and manages to open up a portal to Lucifer's Cage in Hell. Just before Sam jumps into the hole, Michael (still in Adam's body) arrives and begs Sam not to go through with it, as it is his destiny to fight Lucifer. As Sam throws himself into the cage, Michael tries to stop him, only for Sam to pull Michael in as well. As a result, Sam, Adam and the two archangels are sealed away in the cage forever.
In the following season, Dean attempts to bargain with Death to get Sam's soul out of the cage, as well as releasing Adam. However Death states that he can only choose one, and Dean chooses Sam, which leads to his soul being saved but Adam remains behind in the cage with Michael and Lucifer, which he remains to this day.
Adam is mentioned in season 10 during the 200th episode in which fangirls of the Supernatural book series put on a stage production based around the novels. When Sam and Dean fail to recognise one of the characters in the cast, one of the producers points out that it is Adam, and that he is still trapped in Lucifer's cage. This causes both Sam and Dean to give each other an awkward glance at each other.
In Season 11 Lucifer manages to manipulate Sam, Dean and Castiel in order to escape from the cage, which leaves only Michael and Adam remaining. Lucifer later states that Michael has lost his mind due to being in the cage too long, and spends his time singing show tunes and "touching" himself.
Lucifer's claim of Michael being driven insane was supported by God (prior to the revelation of God's true malicious nature). This was later disproven after Sam and Dean discovered that God's only concern was to be entertained. After escaping Hell Michael is shown to be completely sane and on reasonable terms with Adam as his vessel, even showing that the pair are now friends as they were all they had in the cage. Adam is shown to be somewhat bitter and resentful of his half-brothers for leaving him Hell. While he doesn't forgive his brothers entirely he does side with them when they tell Michael the truth about God. Before leaving Michael gives Adam control so Dean can apologize for leaving him, saying he didn't deserve that. Adam then says "When do we get what we deserve" (a reference to all the tragedy their family has endured). In Inherit the Earth, Michael reveals that God killed Adam along with the rest of humanity. Michael, still using Adam's body as his vessel, is noticeably upset when informing the Winchesters and Jack of this development and even states that Adam is gone "sadly."
- For ten seasons, Adam was trapped in the cage along with Michael. In that time, there was some fan demand for the character to be brought back and given proper closure (as it was seen as unfair that he had been left to suffer for eternity in the cage), with even the cast members voicing their hopes for it to be wrapped up. He eventually returned in season 15 along with Michael when the pair escaped the cage, having been trapped for nine to ten years on Earth (which in Hell is approximately 1080-1200 years, meaning that from Adam and Michael's perspective the pair had been trapped for over an entire millennia).