Azrael, AKA, The Angel of Death, or, Lazaer, is a Marvel Comics villain and an enemy to anyone who denies death's natural rules, like Wolverine.
Azrael is also known as the Angel of Death. He sends souls to the afterlife and murdered people who don't follow to death's natural rules, whether being cheating death or killing people before their time.
If any his opponent somehow managed to kill him, they would fight him again in Purgatory if his opponent died. This is for the chance to escape the afterlife if they won in Purgatory. Most of the people who were able to beat Azrael twice would become trapped in their earth-bound undead corpses. One of the few exception is Wolverine, due to his accellerating healing factor.