C'Thul is one of the 5 Elder Old Gods exiled to the Far Realms by the Gods at the end of the Dawn War. From his domain in the inky black, C'Thul slithers between the cracks of reality, manipulating mortals into serving his own alien intentions. Of the Elder Beings, C'Thul is the oldest, and only one of his brothers not imprisoned on Erasis, fleeing into exile at war's end rather than be captured.

The entity known as C'Thul is said to take many shapes, his true form being beyond mortal comprehension, most images of C'Thul are made in the image of his most devoted supplicants, the Illithids.