Etrigan

Jason Blood is a world leading expert on the occult and demonology. He has walked the Earth since the 6th Century, after the wizard Merlin bound the increasingly uncontrollable threat of Etrigan The Demon to his mortal soul.

Etrigan is a demon of Hell bonded to a man named Jason Blood, who usually acts on the side of good despite his violent tendencies. They were bonded together in Camelot by the wizard Merlin as a punishment, imprisoning Etrigan and making Blood effectively immortal. Despite sharing the same body, they are usually at odds with each other and Blood retains a lot of guilt based on Etrigan's demonic actions. Etrigan's most distinctive trait is his skill at speaking in rhyme, a symbol of his social status in Hell's aristocracy. He is the leader of the Demon Knights and has been involved with the Justice League.