Ghatanothoa the Dark God appears in H. P. Lovecraft and Hazel Heald's story "Out of the Aeons". It is a huge, misshapen monster whose form is so hideous that merely seeing it transforms the viewer into a petrified body with leathery skin and preserved organs. The victim's brain remains alive, going mad from its confinement.
Ghatanothoa lived in the mountains of Mu when that continent existed, having arrived or been brought there from Yuggoth. It was worshipped by a hundred priests, who possessed great privileges. The job of these priests was to appease the monster so that it would not emerge from its secret lair, endangering the people.
In the "Year of the Red Moon", T'yog, a priest of Shub-Niggurath, attempted to save mankind from Ghatanothoa. He created a magical scroll to protect him from Ghatanothoa's petrifying power by prayer to Shub-Niggurath, Nug and Yeb, and other deities. With this, he believed he could physically encounter the god and force it to parlay with him. He believed that this could gain him immense power, as well as benefiting the human race. The priests of Ghatanothoa replaced it secretly with a powerless imitation. Thus, T'yog too was petrified into a half-living statue, which lasted up until the modern era.
According to Colin Wilson's story "The Return of the Lloigor", Ghatanothoa, the "dark one", was the leader of the lloigor, an alien species.