Cthulhu, also known as Cthulhutl, Ktulu, Kthulhut, Tulu, Kutulu and Q'Talu. High priest of the Great Old Ones and one of the most infamous of those alien beings. He is said by some to resemble a huge, bloated humanoid with an octopoid head, claws, and great bat-like wings. Cthulhu is more or less immortal, capable of reforming after any attack (even a nuclear explosion) and is possessed of great powers that resemble magic.
Cthulhu is said to have come to Earth some 350 million years ago from the star Xoth. Near Xoth, he had mated with Idh-yaa to produce the triad of Ghatanothoa, Ythogtha, and Zoth-Ommog. He also spawned Cthylla, a female entity that is said to be the source of his rebirth were he ever slain. All four of these younger Old Ones came with him to Earth. He is said to have an enmity for Hastur, who is supposedly his "half-brother."
Cthulhu and his servants, the Star-Spawn of Cthulhu, built the city of R'lyeh and attempted to dominate Earth. However, they became embroiled in a war with the Elder Things, the current rulers of the planet. Eventually, they made peace.
Following the war between the Old Ones and the Elder Gods, Cthulhu was trapped in deathless sleep in R'lyeh, which sunk beneath the Pacific Ocean. Despite that, Cthulhu has since been worshipped by a world-wide cult, as well as by the Deep Ones. When R'lyeh surfaces (as it does on occasion), Cthulhu's dreams can touch sensitive minds, inciting madness and violence. One day, when the stars are right, R'lyeh will rise permanently, and Cthulhu and his spawn will dominate the world once more.
The Ghostbusters stopped a Manhattan-based cult from summoning Cthulhu on Coney Island. Curiously, he was red-skinned in this appearance and could be dispersed by lightning, contradicting the majority of accounts about him.