There was once only a single race of 'Serpent Beings'. Then, for reasons unknown they split into two factions: the snake-headed Serpent-Man, and the Man-Serpents; huge snakes with the mask-like human faces, and venomous little serpents for hair. Under the command of Thoth-Amon, for a time, they warred with the Serpent-Men who were ruled by Thulsa Doom. Eventually both came to serve the wizard from Stygia.