Orcus

Orcus is a very old demon. Like many of the most powerful demon lords who struggle for power in the Abyss, Orcus started his existence as a mortal on the Prime Plane. He was apparently a wicked spellcaster of some sort, most probably a priest to some dark deity. After his death, his soul, like the souls of all chaotic evil mortals, went to the Abyss and Orcus began his afterlife as a lowly larva.
Orcus proceeded to climb through the demonic ranks in the next several thousand years, going from larva to mane, then on to dretch, rutterkin, vrock, glabrezu, nalfeshnee, and eventually a balor. From there, he ascended to the rank of demon lord, becoming the Prince of the Undead and ruling the layer of Thanatos, the Belly of Death. Even though there are other demon lords aspiring to the title of “Prince of the Undead”, Orcus’ claim to the title has gone unchallenged for the most part. Ever hungry for more power, Orcus wanted to be recognized as “Prince of Demons”, a title held by Demogorgon and coveted also by Graz’zt. As a result, he became the arch-enemy of both demon lords. In time, Orcus also achieved true godhood.
However, shortly after his divine ascension, Orcus was slain by the drow demi-goddess Kiaransalee, who took over rulership of Orcus’ layer of the Abyss and locked his wand away in the last layer of Pandemonium. Kiaransalee decreed that Orcus’s name be erased from all existence.
A peculiar combination of events thwarted Kiaransalee’s plans. Acererak’s tampering with the nature of the Negative Energy Plane, the last prayers of Quah-Nomag, and the unexpected awakening of some of the sleepers of the demiplane of Moil combined to cause the spirit of Orcus to be reanimated as an undead god. Renaming himself Tenebrous in order to help obscure himself from his enemies, he traveled to ruins buried in the sands of Pelion. There, he discovered the Last Word, an utterance so powerful that it can destroy deities. The Last Word will also eventually kill those who know it unless the being is a true deity. Thus, to restore his lost divinity, Tenebrous went in search of his wand. During his search, Tenebrous killed several gods and other powerful entities, including Bwimb, Primus, and Maanzecorian. Tenebrous’s efforts were stymied by a group of adventurers and he was again destroyed, this time by the power of the Last Word. A cabal of greater deities, in response to Tenebrous’s predations, has since weakened the Last Word considerably.
Orcus was resurrected by Quah-Nomag, one of his foremost high priests and thralls, in a blasphemous ritual enacted in the Astral Plane. Orcus then reclaimed his kingdom and his original name, re-proclaiming himself “Prince of the Undead”. However, as a result of his second death and resurrection, Orcus has lost his divinity and the ability to use the Last Word, and is a demon lord once more.
Orcus’s divinity now exists as a vestige, also named Tenebrous: The Shadow That Was, and can be called upon by binders.

Unlike many of the other demon lords of the Abyss, Orcus has a widespread cult on the Material Plane. The cult of Orcus is mainly composed of twisted creatures with a morbid fascination with the undead, such as necromancers, as well as creatures deliberately seeking the path to undeath, such as would-be liches and vampires. They often wear macabre costumes decorated with bones and skulls; blood and skulls feature prominently in imagery devoted to him.
Orcus

Orcus

Vale of Darkness NickPassaro