William found out Vincent, his demon, was the prince of hell...until Caster Stixle, or Lucifer, Bradley's father, killed Vincent's parents and threw him out of hell.. leaving Vincent alone...well almost...he had a companion...Morpha...

The demons had him de-clawed, due to the poison in his claws... So, when Vincent went inside, William's dead corpse, and brought him back, he brought Morpha...

Morpha loved The Afton's and decided to stay..