What Is Yog-Sothoth?

Yog-Sothoth is filed as an Outer God, and the dossier describes it less as a being with a location than as a condition of existence: an entity coterminous with all time and space, appearing, when it appears at all, as a mass of iridescent, shifting spheres. The Archive enters it under the names the Lurker at the Threshold and the Opener of the Way, because what it is said to do is open a gate between this world and the space beyond it, and to guard that gate.

The gate

That is the sense in which the witnesses use its name, and the sense in which the cult at Dunwich invoked it. A formula containing the name is what Wilbur Whateley was looking for when he came to the Library at Miskatonic University to compare his own defective copy of the Necronomicon with the University's Latin text. The ritual he wished to complete depended on the passage.

Offspring

The dossier notes one thing that sets Yog-Sothoth apart in the record: it can father offspring on mortals, under the right ritual conditions. Wilbur was one such child. His twin, kept hidden in the family barn and only distantly related to a human shape, was the second, and the more immediate danger to Dunwich after Wilbur's death in August 1928. The account of how it was ended is in The Dunwich Horror.

The other appearance

The name returns in Through the Gates of the Silver Key, the sequel to The Silver Key, where Randolph Carter's journey beyond the Ultimate Gate brings him to Yaddith, a locality the Archive files UNLOCATABLE because it is another world entirely. That chronicle is the single co-written account this office carries, filed as an exception on the strength of its place in Carter's record.