Errtu is a balor tanar'ri, and was featured as a secondary villain of the first book in the Icewind Dale Trilogy,The Crystal Shard by R. A. Salvatore, and was the main villain of Passage to Dawn, the final book in Salvatore's Legacy of the Drow series. He commands his own layer of the Abyss and the tanar'ri inhabitants who reside there
Errtu is a balor, the second most powerful class of the true tanar'ri (chaotic evil demons), after the demon lords. He is twelve feet tall (according to Salvatore's Siege of Darkness), covered in red scales, with a large pair of batlike wings and a tail, and is frequently described as having a horned, ape-like head with a doglike muzzle. When he's in the throes of lust for power, he drools an acidic saliva. His voice is gravelly, guttural, and harsh. He is the ruler of a layer of the Abyss characterized by the growth of giant mushrooms, and even has a throne carved into the stalk of one. His weapons are usually a many-tailed whip, a sword of lightning, and his considerable magic and wits.