Yet another son of Lord Cthulhu. This one is 'the abomination in the abyss. And is chained by the Elder Sign in Yhe, the location of which the Wilmarth Foundation has not, as yet, pinpointed.
This all featuring in Brian Lumley's Cthulhu mythos stories. Ythogtha does not, that I have seen, feature in any of the stories, and is only given a passing mention - along with his brothers Ghatanotha and Zoth-Ommog - in 'The Transition of Titus Crow', chapter 5. His sister Cthylla is given rather more coverage in the book.