Yog-Sothoth, also known as "The Key and the Gate," "The All-in-One," "The Hidden One," "The Opener of the Way," and "The color that came from space," is a fictional character in the Cthulhu Mythos. Created by Howard Phillips Lovecraft, Yog-Sothoth first appeared in his novel "The Case of Charles Dexter Ward" in 1927. Described as a conglomeration of shining spheres, Yog-Sothoth is a powerful being with vast knowledge of time and space.

In Lovecraft's works, Yog-Sothoth is depicted as an outer god responsible for bringing back the primordial beings. It is said that Yog-Sothoth knows the entrance, is the entrance, and is the key and guardian of the entrance. Past, present, and future are all one in Yog-Sothoth, as described in "The Dunwich Horror."

Yog-Sothoth is one of the Outer Gods connected to all time and space, although supposedly trapped outside the universe we inhabit. This deity knows and sees everything, and seeking its favor can bring knowledge of many things. However, delving too deep into its mysteries often leads to disastrous, sometimes fatal, consequences. Some authors suggest that gaining Yog-Sothoth's favor may require a human sacrifice or eternal servitude to the god.