Tenebrous

Tenebrous is a demon lord and master of the undead. Once serving The Dark End until he was betrayed by the Demon Lords and its essence and soul trapped within Heartcleaver in an act of loyalty to the Dark End and betrayal to Tenebrous.

Description
Orcus was typically described as having the head and legs of a goat, although with ram-like horns, a bloated body, bat-like wings, and a long tail.

History
Like many of the most powerful demon lords who struggled for power in the Abyss, Tenebrous 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 Tenebrous began his afterlife as a lowly larva.

Tenebrous proceeded to climb through the demonic ranks over the next several thousand years, going from larva to mane, from mane to dretch, from dretch to rutterkin, from rutterkin to vrock, from vrock to glabrezu, from glabrezu to 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", Tenebrous' claim to the title went 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.

Following his entrapment into Heartcleaver, he would eventually find his way into the hands of the Adventurer's Guild of Eskarya, making a pact with Barandir to aid their hunt of the Demon Lords. When the guild visited the Black Lotus Monastery, and Zalmoxon was slain, Tenebrous had gained enough power form devoured souls to release himself from his prison and attack the final Demon Lord, Yolgoruth.

Upon the guild's escape, they left the Demon Lord trapped into the demi-plane. The fate of Tenebrous is now unknown, but believed to have returned to the Abyss.