Wikipedia
Errtu
Errtu is a balor, a true tanar'ri ( chaotic evil demon) in the Dungeons & Dragons role-playing game, chiefly in the Forgotten Realms campaign setting.
Errtu was featured as a villain of the first book in the Icewind Dale trilogy, The Crystal Shard by R. A. Salvatore, and the main villain of Passage to Dawn, the final book in Salvatore's Legacy of the Drow series. Second to the assassin Artemis Entreri and Obould Many-Arrows, Errtu is the greatest nemesis and most powerful and dangerous foe of the drow renegade, Drizzt Do'Urden, though Errtu has described himself as 'he who hates Drizzt most'.