Lucifer (Proverbs 17:3)

Lucifer is an archangel that exists in an alternate universe.

Early History
At some point in time, Lucifer's true vessel, Sam Winchester said yes to him. Some time later, he is confronted by his vessel's brother, Dean, who unsuccessfully attempts to kill him with the Colt. After this failed attempt on his life, Lucifer burns Dean to death.

Season 15
In Proverbs 17:3, due to Sam's shared wound with God, he saw a memory of an alternate universe where he said yes to Lucifer.

Appearances

 * Season 15
 * Proverbs 17:3