Cthulhu is a being.
August Derleth, a correspondent of Lovecraft's, used the creature's name to identify the system of lore employed by Lovecraft and his literary successors, the Cthulhu Mythos
:256According to Derleth's scheme, "Great Cthulhu is one of the Water Elementals" and was engaged in an age-old arch-rivalry with a designated air elemental, Hastur the Unspeakable, described as Cthulhu's "half-brother

