Nightbringer

The Nightbringer is the demon lord of undeath. He is a towering, catlike creature with glowing red eyes, long, white fangs, and steel claws. His thick, black coat is streaked with red.

History
In the distant past, the entity known as the Nightbringer was trapped within a longsword. With the power to devour the souls of those it slew, the blade Nightbringer changed hands many times over the ages before coming into the possession of Zirithian, a drow who sought to become an exarch of Orcus. Nightbringer was claimed by the Challengers of the Unspeakable upon the death of its owner. Orcus appeared and demanded the blade, but the sword spoke to them, urging them not to give it to the demon lord. When it promised Harthur Grai the power to slay his foes in combat, the ranger decided instead to keep it for himself.

After Harthur disappeared into the Abyss, the wizard Jorlin reported seeing it in the hands of a balor when attempting to scry on the blade; this report was cast into doubt, however, when it was discovered that Jorlin had been replaced by the doppelganger Gix.

In truth, Harthur had survived and used Nightbringer to cut a bloody swathe through the White Kingdom and into the citadel of its ruler: Doresain, King of the Ghouls and devoted servant of Orcus. Harthur confronted Doresain in combat, slew him, and fed his soul to Nightbringer. When Orcus opened a portal to summon Doresain to aid him in battle against the Challengers of the Unspeakable, Harthur emerged and instead helped them against Orcus, ravaging the demon lord with Nightbringer before ultimately plunging the blade into his stomach. The Nightbringer immediately took the opportunity to leave the sword and enter Orcus, devouring his soul and emerging from his corpse in a new physical body.

The Nightbringer claimed Orcus's former title of demon lord of undeath, as well as his position as ruler of Thanatos, and named Harthur first among his exarchs, granting him control of the White Kingdom and the armies of demons and undead therein. As a reward to the Challengers of the Unspeakable for aiding his exarch against Orcus, the Nightbringer agreed to retrieve Kayleth Lifesinger from Oublivae's clutches.

He then departed with Harthur back to the Abyss to consolidate his power.

The sword
When it was still trapped in the blade, Nightbringer spoke aloud in a hoarse whisper and exhibited a certain level of awareness of its surroundings. Even after the Nightbringer manifested a new physical form, though, the sword still retained its magical properties. It grants its wielder protection against undead creatures in combat, and is capable of taking control of weaker undead.

Perhaps its most notable property, though, is that it consumes the souls of creatures killed by it. While the Nightbringer was still imprisoned within the blade, he devoured the souls to gain power; now that he has attained physical form, it is unknown what happens to the souls consumed by the blade. Some of the more notable souls fed to the Nightbringer are those of Matron Urlvrain, ruler of the drow city of Phaervorul; Rukaleth, a red dragon; Doresain, King of the Ghouls; and the demon lord Orcus.