|“||Don't you think that your brother dragged you back into that catastrophic mess because he'd rather damn you with him than be alone?||”|
Osiris is the Egyptian god of the afterlife, transition, death, life, the dead, resurrection, regeneration, fertility and ruler of the underworld. He put people who feel guilty on trial, and sentenced them to death and commanded ghosts or specters to carry out the sentence.
Osiris went to a local bar where he found people who felt guilty. He later grabbed Matthew Hammond, Christopher Fisher, and Warren and took them to his court where he held a trial and condemned them. Dean Winchester bumped into him in a bar, where Dean told his guilt to the bartender.
After Dean left the bar, Osiris abducted him. Dean was taken to a farm where he was put on trial by Osiris. Sam acted as Dean's lawyer in the trial. Osiris called three witnesses: Jo Harvelle, Sam and Dean himself. In the end, Dean was found guilty and Osiris told him that he would die soon. Just before Dean could be killed, Sam stabbed Osiris with a ram's horn and put him into a centuries-long sleep while freeing Dean from death. However, Dean continued to feel guilty about his past action, including lying to his brother about Amy Pond.
It's revealed by Castiel that after God abandoned Heaven, Osiris was considered for the job as the new judge of souls. However he was passed over in favor of his son Anubis. Dean also remembers the Winchesters meeting with Osiris and comments upon it. 
Powers and AbilitiesOsiris is a powerful deity, harnessing many abilities and few weaknesses.
- Invulnerability - As an ancient Egyptian deity, the only known thing that can harm him was a ram's horn.
- Telekinesis - The power to move things with his mind.
- Biokinesis - Was able to stop Dean from speaking, with a gesture.
- Teleportation - He could casually move from place to place in the blink of an eye, he could also teleport others from one place to another with a gesture.
- Super Strength - He was strong enough to overpower several grown men, with no difficulty.
- Immortality - As a deity, Osiris could live forever and nothing is known to be able to kill him.
- Super Senses - Osiris knew Sam was present despite his attempts to hide.
- Telepathy - He was able to read others' minds to learn their guilt, and bring it forward to them.
- Necromancy - As god of the dead and the underworld, he could summon the dead, and force them to do things against their will. It was implied that he can control the ghosts of monsters as well.
- Ram's Horn - Being stabbed by a ram's horn will put Osiris to sleep for a couple of centuries. It is not permanent, however.
- Osiris is usually portrayed as a bearded, mummified human with green skin and wearing the atef crown. His hands emerge from the mummy wrappings and holding the flail and crook.
- Osiris' real-world wife Isis appeared in "Hammer of the Gods". Their relationship in the series is never stated.
- Writer Adam Glass did not particularly like Osiris which made writing the character difficult.
- Osiris' son, Anubis, would appear in "Byzantium". Their relationship with each other is unknown.