Tanar'ri

The most widespread race of fiends are the demons, a chaotic evil race native to the Abyss; they are rapacious, cruel and arbitrary. The dominant race of demons is the tanar'ri. The Abyss and its population are both theoretically infinite in size. "True" tanar'ri such as the balors (originally called Balrogs) and the six-armed serpentine mariliths push other weaker tanar'ri around and organise them into makeshift armies for battle. Demon lords and demon princes such as Lolth, Orcus, Demogorgon, Zuggtmoy, Graz'zt and countless others rule over the demons of their individual layers of the Abyss, inasmuch as the chaotic demons can be ruled over.

In First Edition Advanced Dungeons & Dragons, some types of demons were not given species names, but were rather referred to as "Type I" through "Type VI" demons. In subsequent editions, Types I-VI were instead known as Vrocks, Hezrou, Glabrezu, Nalfeshnee, Mariliths, and Balors, respectively. Some of these names were originally given in the First Edition Monster Manual as example names of specific demons of that type, so (for instance) Marilith was the originally the name of an individual Type V demon.