Ymuz

Ymuz, the Vile, The Mother of Abomination, from whom all monstrosity descends, was one of the Old Gods or the Aiyu-Atma and was unquestionably the most evil, hateful, hideous, and loathsome among them. She was the unholy consort of Chogorus, though she also mated with Khyron and Kharax many times. By them, and by others too, and from the fecundity of her own foulness, she spawned the myriad dark gods of Karkharos along with innumerable lesser demons, fiends, devils, and monsters. In the end she was consumed by Chogorus and thereby destroyed, meeting oblivion at last in the gut of the Great Devourer, although the evils that came forth from her still trouble the world.
The countless loathsome children of Ymuz are collectively known as the Ymuzu-Vaati.