Ythogtha is the second son of Cthulhu in Lin Carter's Xothic Legend Cycle, which centers on a trinity of deities said to be the "sons" of Cthulhu — spawned on a planet near the double star Xoth from a mating between Cthulhu and the quasi-female entity Idh-yaa.
He resembles a gigantic, humanoid frog or Deep One with only a single eye in the center of his forehead, like a cyclops; a dense mane and a beard of writhing tentacles grow from his head. He was imprisoned in the Abyss of Yhe by the Elder Gods.
He is served by the planarian-like yuggs and their lord, Ubb, the Father of Worms. His legend first appears in Lin Carter's "The Dweller in the Tomb" (1971).