Azazel (Anime Series)

Azazel (アザゼル), also known as the Yellow Eyed Demon, The Demon, and The Devil, was the main antagonist of Supernatural: The Anime Series, an animated Japanese remake of the first two seasons of the original TV series. He was once an angel in Heaven before falling from grace and becoming a demon. He was the demon that killed Mary Winchester, and these actions caused John Winchester to pursue Azazel for the rest of his life. Azazel fed his blood to an infant Sam Winchester, transforming him into a Special Child. Azazel was killed with The Colt by Dean Winchester.

Appearances
The Alter Ego (in Sam's nightmare)

Trivia

 * In this version, Azazel was originally an Angel before becoming a Demon, while in the live action TV series, he was presumably a Human soul that was tortured and corrupted in Hell as other Demons were.
 * In this version it would seem that Azazel was also the devil however it can not be confirmed though when called the Devil he never denied it.