Orcus is the Demon Prince of the Undead. He is not a god but a powerful lord of the abyss. His main goal is the death of the Raven Queen, he is revered and worshiped by the undead themselves.
An Aspect of Orcus was recently killed in battle with the powerful Bugbear known as Gulohg. Gulohg was wielding Necradur, a Morganti sword. Learned scholars believe that this sword has swallowed the soul of the Lord of the Dead creating a vacuum in the power balance of the realms.