Yog-Sothoth exists in all times and places at once; past, present, and future are a single point to it. Lying at the boundary between dimensions, it is called "the Gate and the Guardian and the Key."
Those who chase forbidden knowledge try to unbar the universe through Yog-Sothoth, but the opening always devours the one who opens it. The tragedy of "The Dunwich Horror" is the archetype.