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Official Site: H.P. Lovecraft

Yog-Sothoth is a cosmic entity in the fictional Cthulhu Mythos and Dream Cycle of American horror writer H. P. Lovecraft. Yog-Sothoth's name was first mentioned in Lovecraft's novella, The Case of Charles Dexter Ward (written 1927, first published 1941). The being is said to take the form of a conglomeration of glowing sphere.

Imagination called up the shocking form of fabulous Yog-Sothoth — only a congeries of iridescent globes, yet stupendous in its malign suggestiveness.

—H. P. Lovecraft, "The Horror in the Museum"

Yog-Sothoth is an Outer God and is coterminous with all time and space yet is supposedly locked outside of the universe we inhabit. Its cosmic nature is hinted at in this passage from "Through the Gates of the Silver Key" (1934) by Lovecraft and E. Hoffmann Price:

Yog-Sothoth has not been a contender in any CBUB matches.