Orcus, Lord of Rot

Few names conjure as much Dread as that of Orcus, and few Demons command as much respect and Worship as the Lord of Rot. The Tale of Orcus is long, twisted, and tangled, with many a Rise to Power, and many a Fall. It is said that Orcus was once a man, evil to his very core, and as such his soul fell to the Abyss, where he wormed his way through the ranks to the very top, becoming a Demon Lord.
Orcus fought for the title Prince of Demons, nearly claiming it for himself. Once he even briefly gained Divinity, a minor God of Undeath and Decay, but he was usurped, and even killed. Not entirely unheard of amongst Gods, the Timescape is littered with the bodies of Fallen Gods, and even the Great Bahamut was killed. But Orcus did not stay dead. Like a true aspect of Undeath he rose, and fought his way back, reclaiming his former power. But he was changed, and no longer a true contender for the Prince of Demons. Demogorgon solidified the title, and Orcus had not the power he once enjoyed.
Yet, his new circumstances also gave him opportunity. He was still a Demon Lord, yes, but he was something else too. Somehow he was simultaneously Demon and Undead, and the Unlife that gave him power was drawn to him even more. So, he took advantage. The Undead have no souls, and as such Demons hold little to no power or contempt for them. And Orcus was now a conduit for Unlife, a True Ruler of Undeath, a Lord of Rot...
So Orcus did the unthinkable. He left the Court of the Deep, returning to his Realm deep within the Abyssal Wastes. He repurposed the city of Thanatos, his Ancient Stronghold, into haven of Unlife, a city rivaling that of the Seven Cities of Baator. He formed the Court of Decay, a haven for the Undead, where he could amass his legions away from prying eyes and meddling factions. The other Demon Lords resented this, hated it, but little could be done. The Undying were strangely well suited for battle against the Demons, and Orcus's Aura and Influence brought endless hordes that could match the Demons. So they stayed locked in a stalemate, neither side able to gain ground. Orcus would never be Prince of Demons, nor rule the Abyss, but neither would the Abyss be rid of him.