Demon Lord of Undeath, the Blood Lord
Orcus was the demon lord of undeath. One of the most powerful demons in the Abyss, Orcus sought total control over death and undeath alike; as a result, he was a long-time nemesis of both Nerull and Wee Jas. With their deaths during the Deity War, Orcus set his sights on the Raven Queen, the only being who still stood between him and complete dominion over death.
In 2959, Orcus entered into an alliance with the wizard Tephra; in exchange Nerull's scythe, Lifecutter, his forces would aid her in helping Allabar enter Syra. The demon lord quickly grew impatient, however, and when Oublivae's machinations created a rift from the Abyss to the Material Plane, he stepped through to personally claim the scythe for himself. When he encountered the Challengers of the Unspeakable, who had recovered it from Tephra's minions, Orcus opened a portal and called upon his exarch, Doresain, for aid. Instead, however, the death knight Harthur Grai emerged from the portal, having slain Doresain and claimed rulership of the White Kingdom for himself. Now, he stood with the Challengers to slay Orcus.
After a pitched battle with the demon lord, Harthur plunged the sword Nightbringer into his belly. Shadowy magic coursed out of the blade into Orcus as the entity trapped within the blade flowed into a new host. Orcus's body tore apart, utterly consumed to fuel Nightbringer's rebirth as the new demon lord of undeath.