Michael

Michael is God's strongest archangel and was formerly the Commander and Chief of God's Army. He is the oldest brother of Lucifer, Gabriel and Raphael. When Lucifer rebelled, he personally banished Lucifer from Heaven and sent him to Hell as God had ordered him to. When Lucifer was released and roamed the Earth, Michael was seen as the only being other than God that was capable of killing him. When Dean Winchester, his true vessel, refused to allow Michael to possess him, he possessed the body of Sam and Dean's half brother, Adam Milligan. He is currently still possessing Adam and is trapped with Lucifer inside Hell.

Season 5
Michael makes his first appearance in "The Song Remains the Same". After Anna Milton kills Sam Winchester by stabbing him in the stomach, Michael appears before John Winchester and tells him that he can save his wife Mary if he allows him to take possession of his body. John says "Yes," allowing Michael to inhabit his body. When Anna is about to kill Mary, Michael calls out to Anna. Anna turns around and immediately realizes that Michael is possessing John. Michael lays his hand on Anna and kills her by setting her ablaze. Uriel then calls out to Michael and apologizes, saying that "He didn't know," most likely referring to that he didn't know Dean was Michael's true vessel. Michael says goodbye to Uriel and sends him away with a snap of his fingers.

Michael then turns to Dean and says that this conversation is long overdue. Dean demands that Michael heal Sam, but Michael tells him that they need to talk first. Dean asks Michael how he could possess his father since he was his "one and only" vessel. Michael corrects Dean stating that he is his true vessel and that he can inhabit the body of all those that share the Winchester bloodline due to the fact that he and John were descendants of Cain and Abel. He then explains to Dean that even though Lucifer defied their Father and betrayed him, he doesn't want to kill him as much as Dean wouldn't want to kill Sam. Michael then says regardless of the fact that he raised Lucifer and still loved him, he is going to listen to his Father and kill Lucifer. He then explains to Dean that he will eventually say "Yes" to him because free will is an illusion and that his choices, regardless of what they may be, will lead him a step closer to his destiny that was planned out by God.

Michael tells a saddened Dean to cheer up because, unlike his brothers, he won't leave him a drooling mess after he's done "wearing him". He then tells Dean that he will erase John and Mary's memories of the whole incident and that they won't remember anything about angels, him, or Sam. Michael walks over to Sam's body, heals him, and then sends him back to his own time. Michael then walks to Dean, telling him that he'll see him soon before sending him back to his own time.

In the season 5 finale "Swan Song", Michael's appears at Stull Cemetery in Lawrence, Kansas in possession of Adam's body in order to face Lucifer in the final battle of Armageddon. Lucifer tries to convince Michael that they shouldn't fight because God made Lucifer the way he is, because he always wanted the Devil. Michael isn't convinced and the two prepare to fight just as Dean drives down into the cemetery and interrupts them. As Dean tries to talk to Sam, Castiel and Bobby appear and Castiel hits Michael with a holy oil molotov cocktail in order to send him away temporarily. After Lucifer makes Castiel explode and breaks Bobby's neck, he begins to beat Dean. This continues until Sam reclaims control of his body and opens the portal to Hell. Michael returns and tells Sam that he can't jump in because he has to fulfill his destiny by killing Lucifer. Sam then pulls Michael with him as he falls into the portal, trapping Adam and Sam along with Lucifer and Michael in Hell.

Abilities

 * Immortality - There's only a few ways that Michael can die, he can only be killed by Death, God, Lucifer and by any angel with an rchangel blade. Just like the other Angels, he is imune to illness.
 * Superhuman Intelligence - Like his younger brother Lucifer, Michael possess an almost-infinite degree of knowledge of the universe
 * Super Strength - Michael's strength is comparative to Lucifer's (Michael may be a little bit stronger than Lucifer).
 * Teleportation - Michael can teleport himself along with a group of people to any location around the globe.
 * Angelic Possession - Like all angels, Michael needs the consent of his vessel in order to possess the human. Michael's angelic spirit can be very overwhelming to ordinary vessels. Michael's mere essence can burn out any vessel that isn't within the Winchester bloodline.
 * Invulnerability - Michael's invulnerability renders him as an indestructible being. However, Michael can be killed with an archangel sword. Holy Fire can banish Michael to a distant location temporarily. Death's Scythe can kill Michael. Lucifer can penetrate through Michael's angelic invulnerability.
 * Healing - Michael can heal humans from any wound and or injury that they may have.
 * Resurrection - Michael can raise the dead. Due to his healing powers he can then go on to healing the victim's wounds to such a degree that the victim is revived and brought back to life. He demonstrated this ability in episode 13 of the 5th season, "The Song Remains The Same".
 * Time Manipulation - Michael can manipulate/bend time. He proved this when he successfully sent Sam and Dean back to their correct time period. He demonstrated this ability in episode 13 of the 5th season, "The Song Remains The Same".
 * Memory Manipulation - Michael has the ability to take away and restore a human's memories.
 * Pyrokinesis - Michael can generate heat from his body and can then emit the heat out

Relationships

 * God (Father & Boss)
 * Lucifer, Raphael, Gabriel, possibly Castiel (Archangel Brethren)
 * Other Angels (Brothers and Sisters)
 * Dean Winchester (True Vessel) - Dean was later no longer the vessel for Michael as Michael now picked Adam as the vessel. Even though Michael picked Adam for his vessel, Dean is still the true vessel.
 * John Winchester (Temporary Vessel)
 * Sam Winchester (Younger brother's True Vessel; Possible Temporary Vessel) – Due to Sam being a son of John Winchester, that makes him a descendant of Cain and Abel, just like his older brother and father, meaning that it may be possible for Michael to use Sam as a temporary vessel even though he's Lucifer's true vessel)
 * Adam Milligan (Current Vessel) - When Adam was resurrected by the angels, it was confirmed by Castiel in "Point of No Return" that because Adam has the blood of John Winchester flowing through his veins thus making him a descendant of Cain and Abel and also he is a brother of Sam. It wasn't perfect, but it was possible for him to be a vessel for Michael. In Swan Song, Adam was shown as a vessel for Michael for the fight against Lucifer.

Season 2

 * "Houses of the Holy" (first mentioned)

Season 5

 * "The Song Remains the Same" (first appearance, possessing John Winchester)
 * "Point of No Return" (doesn't actually appear, but his presence is known)
 * "Swan Song" (possessing Adam Milligan)

Trivia

 * His name means "Who is like God."
 * Michael is considered the "viceroy of Heaven," meaning the ruler of Heaven in God's stead.
 * He is the only angel in the Bible named as an Archangel; the rest were named in different interpretations of the Bible and other biblical scrolls, or given the title by the Catholic Church. Hence why he is considered THE Archangel.
 * Many exorcisms invoke the name of the Archangel Michael, to defeat and banish the demon.
 * In the final judgment, Michael is shown as the weigher of souls.
 * Michael is the only angel who is also a saint.
 * Michael holds the keys to Heaven and Hell.
 * He is the Archistratege of God ('Archistratege' being a military rank of the highest degree, superior to a field marshal or grand admiral).
 * Michael is known as the 'Prince of the Seraphim' (the Seraphim being the highest order of angels).
 * He is often shown as the angel who spoke to Moses as a burning bush, delivered the Ten Commandments to Moses, and fought with Lucifer over Moses' body and won.
 * In the Apocalypse, Michael leads the army of Heaven and defeats Lucifer and the Antichrist.
 * It is unknown what happens to Michael at the end of Swan Song as he (in Adam's body) fell in with Sam (with Lucifer) into the portal to hell. What happened to him will probably be explained in the next season.
 * He might be the third most powerful creature in the universe Death being first and God being second. There is yet to be any stronger characters to be introduced