Orcus is a demonlord and master of the undead.
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.
Orcus cared for nothing save himself—not even his devotees and undead servants—and focused only on spreading misery and evil. One of his most identifiable symbols was the artifact known as the Wand of Orcus, a skull-topped wand with the power to slay any living being.
Like many of the most powerful demon lords who struggled 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 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”, Orcus’ 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. In time, Orcus also achieved true godhood.