Errtu

Errtu was a powerful balor. He commanded his own layer of the Abyss and the tanar'ri inhabitants that resided there.

Personality
He had a particular interest in gaining power on and from the Prime Material Plane, in particular Toril.

Combat
He carried a vorpal sword that appeared as a bolt of lightning and was resistant to magic.

Crenshinibon and Drizzt Do'Urden
Errtu once worked for the group of liches that created the artifact named Crenshinibon. When it was brought to "life," Errtu was cast back to the Abyss. He originally thought Crenshinibon was destroyed in the same blast.

After he learned that Crenshinibon had not actually been destroyed, Errtu devoted his existence to finding Crenshinibon again. His search for Crenshinibon led him into several altercations with the drow ranger Drizzt Do'Urden, who sought to keep the artifact out of Errtu's hands. The first time, when Errtu was serving as Akar Kessel's general in Icewind Dale in the, Drizzt summoned Errtu, meaning to pose as a drow scout and inquire about Crenshinibon. When Errtu discovered Drizzt's ivory unicorn pendant—the holy symbol of Mielikki—he attacked the drow, surrounding himself with flames and using his whip to catch Drizzt and pull him into the flames. Upon contact with Drizzt, the flames were extinguished by the magic of the as-yet unnamed scimitar Icingdeath. In a confused moment for both of them, Drizzt slashed Errtu with Icingdeath, causing the balor real pain and the blade's magic even froze the tissues at the edge of the wound. Errtu and Drizzt were both shocked, having never even heard of a weapon with such an effect, but Drizzt recovered first and stabbed the balor in the stomach. The scimitar's magic won out, destroying Errtu's material body and banishing him for a hundred years. As his body dissolved, Errtu reminded Drizzt of their long lifespans and promised revenge.

In the, after Drizzt's companion Wulfgar was "killed" by a yochlol summoned by Vierna Do'Urden, the evil goddess Lolth gifted the barbarian to Errtu as a bargaining chip in exchange for his guardianship of Menzoberranzan during the Time of Troubles. Errtu tortured Wulfgar for the next six years. That same year, after the fall of House Oblodra, the house's matron mother, K'yorl Odran, was also given to Errtu as a prisoner.

In the, he released himself from a wizard's circle by using an anti-magic stone he kept in a bag, a leftover from the Time of Troubles. This dispelled the summoner's protective magic circle against evil, which was otherwise flawless, and likewise disabled Errtu's magical abilities. However, Errtu, being very strong physically, did not need them to kill the summoner. That year, the balor gained the artifact Crenshinibon and used it to build a stronghold in the Sea of Moving Ice, a body of water west of Icewind Dale and dotted with icebergs. Despite his dislike of cold, Errtu chose the place because of its natural barriers. He opened a gate to the Abyss and let innumerable lesser fiends through, as well as more powerful demons. Drizzt and his friends managed to fight their way through, and confronted Errtu in an ice cave. This time, Errtu had space to fly, and repeatedly teleported around the room, using his flames to melt nearby ice and fill the floor with water—in which he would periodically thrust his lightning-bladed sword to shock the companions. Drizzt and his friends would have died, had Wulfgar not been inadvertently freed by a younger barbarian via the hammer Aegis-fang and joined the fight. Together, the companions managed to bring Errtu out of the air, where Drizzt struck with Icingdeath and banished him for the second time.

Return to Icewind Dale
In the, Errtu appeared outside the walls of Bryn Shander, seeking Drizzt. The drow warrior Tiago Baenre confronted him and banished him, making himself a hero to the inhabitants of the city. The spot where Errtu was slain was permanently blackened. On that spot, the citizens erected a statue of Tiago with the inscription, "On this spot did Master Tiago slay the demon. And the snows will cover it nevermore."

Although he had tortured her and considered her his toy, K'yorl Odran willingly schemed with Errtu a century later when Lolth plotted to use her as a way to weaken the barriers between the Abyss and the Prime Material Plane. In the, Lolth incapacitated Errtu's rival, Balor, as a favor to him. In exchange, Errtu allowed K'yorl to speak with Kimmuriel Oblodra. She provided him with an incantation to subliminally convey to Gromph Baenre. When Gromph cast the incantation, believing it to be the product of his genius, it weakened the walls of faerzress, allowing demons such as Demogorgon to freely pass into Toril.

Relationships
Errtu was known to cooperate with other evil beings. In 1356 DR, he chose to ally himself with the wizard Akar Kessel on the promise that when Kessel died (which wouldn't be long in Errtu's view, even if Kessel died of old age), he would gain Crenshinibon. In 1358 DR, he became a reluctant ally of the drow goddess Lolth—at first because she could obliterate him if he didn't cooperate, and later because she offered him a chance to gain total, personal revenge on Drizzt.

Errtu was the greatest rival of Balor, the great demon for which the balor race was named.

Background
Errtu was one of the original six named "Type VI" demons, alongside Ndulu, Ter-Soth, Alzoll, Wendonai, and Balor, the greatest of them all. The Type VI demons were later named balors, to refer to their breed of demon as a whole. These demons were listed in the Index of Monster Manual II 1st edition, with reference to Monster Manual 1st edition p. 19, but only Balor is mentioned there.