Kthanid is said to be the "brother" of Cthulhu (which is doubtful, as he is an Elder God). He looks like his sibling but has golden eyes. He resides in a crystal cave on Elysia. It is said that he is as good as his brother is evil. He bears a great hatred for The Great Old Ones for they had killed his family while he lay sleeping.
He first appeared in Lumley's 1975 novel The Transition of Titus Crow, and appeared again in his The Clock of Dreams (1978).