Lucifer?

Lucifer is the Ruler of everyone in Hell. After his Fall he organized Hell and made everyone obey him, shortly after this he was never seen again. It is said, that the Fall damaged him so badly, that he needs an unimaginable long rest from Time to Time, which he currently takes. Most newer Demons even doubt he is alive, Rumors say he has already died, but officially Hell is still waiting for his return. Only alive ones who saw him are the Seven Deadly Sins, Astaroth and Lilith. All the other ones who saw him are already dead.