Asmodeus

Asmodeus is the evil god of tyranny, domination and sin. He is the King of Hell, ruling the Nine Hells of Baator, the Duke of the Ninth, Nessus, and father of Glasya, Duke of the Sixth Hell, Malbolge.

Spoilers:

Asmodeus was once an archangel and exarch serving a god now only known as He Who Was, the god of good and peace and possibly the creator of humanity. Asmodeus betrayed his god, killing him and having the devils erase all knowledge of the god's name for fear that the mere mention of it would revive him. This transformed Baator from the realm of He Who Was to the Nine Hells of Baator, a prison for Asmodeus and the devils.

The King of Hell is described as a 13 ft tall human with dark skin and hair, handsome features, and small horns on his head. His body is covered in wounds that bleed daily, sustained from his fall to Baator. The blood from these wounds is said to spawn devils. His weapon of choice and symbol of his station is the Ruby Rod, a 4 ft long rod bathed in the blood of a thousand mortal sacrifices, quenched in the acid pools of Tiamat and polished with the tears of 777 angels. It is said to have been forged from the same shard that created the Abyss.