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|Cthulhu Mythos character|
Artist's depiction of Yog-Sothoth
|Created by||H. P. Lovecraft|
|Title||Lurker at the Threshold
Opener of the Way
The Nameless Mist (parent)
Wilbur Whateley (son)
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 spheres.
Imagination called up the shocking form of fabulous Yog-Sothoth—only a congeries of iridescent globes, yet stupendous in its malign suggestiveness.
- —Hazel Heald and H. P. Lovecraft, "The Horror in the Museum"
Yog-Sothoth 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:
It was an All-in-One and One-in-All of limitless being and self—not merely a thing of one Space-Time continuum, but allied to the ultimate animating essence of existence's whole unbounded sweep—the last, utter sweep which has no confines and which outreaches fancy and mathematics alike. It was perhaps that which certain secret cults of earth have whispered of as YOG-SOTHOTH, and which has been a deity under other names; that which the crustaceans of Yuggoth worship as the Beyond-One, and which the vaporous brains of the spiral nebulae know by an untranslatable Sign...
Yog-Sothoth knows all and sees all. To "please" this deity could bring knowledge of many things. However, like most beings in the mythos, to see it or learn too much about it is to court disaster. Some authors state that the favor of the god requires a human sacrifice or eternal servitude.
According to the genealogy Lovecraft devised for his characters (later published as "Letter 617" in Selected Letters), Yog-Sothoth is the offspring of the Nameless Mists, which were born of the deity Azathoth. Yog-Sothoth mated with Shub-Niggurath to produce the twin deities Nug and Yeb, while Nug sired Cthulhu through parthenogenesis. In Lovecraft's short story The Dunwich Horror, Yog-Sothoth impregnates a mortal woman, Lavinia Whateley, who then gives birth to twin sons: the humanoid Wilbur Whateley, and his more monstrous unnamed brother.
The in-universe essay In Rerum Supernatura in the Call of Cthulhu role-playing game offers a suggestion: Yog-Sothoth's name may be a transliteration of the Arabic phrase "Yaji Ash-Shuthath," more properly "yajī'u ash-shudhdhādh" يجيء الشذاذ, meaning "The abnormal ones are coming." 
In Anders Fager's short story "Grandmothers Journey" a tribe of dog or wolf-like humans (analog to the "ghouls" of the Lovecraftian mythos) is said to have sacrificed to Yog-Sothoth to become "different". In Fager's "Herr Goerings Artifact" Yog-Sothoth is invoked to protect a couple of witches from Father Dagon.
At the end of Lovecraft's late story The Haunter of the Dark, the protagonist Robert Blake calls on Yog-Sothoth to save him from the eponymous malign entity which he has let loose.
The Old Ones
Yog-Sothoth knows the gate. Yog-Sothoth is the gate. Yog-Sothoth is the key and guardian of the gate. Past, present, future, all are one in Yog-Sothoth. He knows where the Old Ones broke through of old, and where They shall break through again. He knows where They have trod earth's fields, and where They still tread them, and why no one can behold Them as They tread.
- —H. P. Lovecraft, "The Dunwich Horror"
Yog-Sothoth has some connection to the mysterious Old Ones mentioned in "The Dunwich Horror" (1929), but their nature, their number, and their connection to Yog-Sothoth are unknown. Nonetheless, they are probably allied to him in some way, since Wilbur Whateley, the half-human son of Yog-Sothoth, tried to summon them so that they could control Wilbur's more tainted twin and make it reproduce.
In The Case of Charles Dexter Ward, its name is part of an incantation that could revive the dead (and with some of the syllables reversed, slay the creature raised):
Avatars of Yog-Sothoth
Aforgomon is an obscure avatar of Yog-Sothoth invented by Clark Ashton Smith. He was revered by many cultures past, present, and future as the God of Time because of his preternatural ability to manipulate time and space. Little is known of this being's appearance because he only reveals himself to those who have angered him. However, it is known that he is accompanied by a blinding light. He is the mortal enemy of Xexanoth.
The Lurker at the Threshold
...great globes of light massing toward the opening, and not alone these, but the breaking apart of the nearest globes, and the protoplasmic flesh that flowed blackly outward to join together and form that eldritch, hideous horror from outer space, that spawn of the blankness of primal time, that tentacled amorphous monster which was the lurker at the threshold, whose mask was as a congeries of iridescent globes, the noxious Yog-Sothoth, who froths as primal slime in nuclear chaos beyond the nethermost outposts of space and time!
'Umr at-Tawil (Arabic عمر الطويل) The [Most Ancient and] Prolonged of Life), also spelled Tawil At-U'mr or Tawil-at'Umr, is described as an avatar of Yog-Sothoth in the story "Through the Gates of the Silver Key", by Lovecraft and E. Hoffman Price. In the story, he presides over the timeless halls beyond the Gate of the Silver Key and the strange, near-omnipotent Ancient Ones that dwell there. He is described as the silhouette of a man behind a strange, shimmering veil. He is one of very few apparently benign Lovecraftian Great Old Ones who does not cause insanity in those who view him.
The Eater of Souls
"...That the chief of these beings is referred to in the Pnakotic Manuscripts and the Eltdown Shards as Iok Sotot, "Eater of Souls," suggests that it was some energy or psychic vibration of the dying victim that the lloigor needed... ". "...in private, of course, they worshipped Iok-Sotot, who became the Yog-Sothoth of the Necronomicon.".
This identification is carried forward in Grant Morrison's Zenith series for 2000 A.D., and in Charles Stross' novelette A Colder War where the entity if summoned is able to instantly consume the minds of entire planets:
...There is life eternal within the eater of souls. Nobody is ever forgotten or allowed to rest in peace. They populate the simulation spaces of its mind, exploring all the possible alternative endings to their life. There is a fate worse than death, you know...
- Lovecraft, H. P. (1967). Selected Letters of H. P. Lovecraft IV (1932–1934). Sauk City, Wisconsin: Arkham House. "Letter 617". ISBN 0-87054-035-1.
- Petersen, Sandy and Willis, Lynn (1992). “In Rerum Supernatura”, Call of Cthulhu, 5th ed., Oakland, CA: Chaosium, pp. 189–92. ISBN 0-933635-86-9.
- Harms, Daniel & Gonce, John Wisdom (1998). The Necronomicon Files. York Beach, Maine: Red Wheel/Weiser, LLC. p. 109. ISBN 1578632692.
- These 'alternate' spellings are solecisms. The Arabic language definite article al only takes the assimilated form at before a word beginning in t. The form should be Tawil al Umr. For a similar error see Frank Herbert's Dar es Balat (were it proper Arabic it would be Dar el Balat) which is erroneously formed by analogy from Dar es Salaam in which the article es is assimilated to the initial /s/ of Salaam.
- Wilson, Robert Anton and Shea, Robert. The Eye in the Pyramid pp.300-301
- The Eye in the Pyramid p.127
- Harms, Daniel (1998). "Yog-Sothoth". The Encyclopedia Cthulhiana (2nd ed.). Oakland, CA: Chaosium. pp. 345–7. ISBN 1-56882-119-0.
- Pearsall, Anthony B. (2005). "Yog-Sothoth". The Lovecraft Lexicon (1st ed.). Tempe, AZ: New Falcon. pp. 438–40. ISBN 1-56184-129-3.
- Petersen, Sandy; Lynn Willis; William Hamblin (1992). "In Rerum Supernatura". Call of Cthulhu (5th ed.). Oakland, CA: Chaosium. pp. 189–92. ISBN 0-933635-86-9.