Yog-Sothoth is an Outer God, and "father" of Cthulhu, Hastur and Vulthoom (according to some). Also known as Iog-Sotot and Tawil at'Umr. He generally manifests as a cloud of iridescent spheres, though he has taken different forms at different times. Those who worship him can gain limited control over time and space, at the cost of their souls.
Yog-Sothoth is identified as the being who spoke to Randolph Carter, once the latter passed through the Ultimate Gate. He posseses ultimate power over time and space. Some say he was a spawn of the Nameless Mist, but others say he has always existed. It is most likely humanity will never discover the true nature of this mysterious god.
Doctor Who (Expanded Universe)
The Great Intelligence is identified with Yog-Sothoth.
When H.P. Lovecraft ever identified what later authors called his "Cthulhu Mythos," he would call it his "Yog-Sothothery," after this creation.