Yog-Sothoth

Yog-Sothoth is a vastly powerful demonic entity from the works of Lovecraft and is known as an Outer God - making it more powerful than the famous Cthulhu and a truly cosmic menace that is beyond mortal comprehension.

History
According to the mythology of Lovecraft Yog-Sothoth is a limitless cosmic horror that is connected with all of space and time yet is locked away from mainstream reality - the monstrous deity sees all and knows all and can impart knowledge to any foolish enough to seek its favor, which often required human sacrifice or worse and would ultimately bring calamity and ruin to the would-be-follower.

To truly put Yog-Sothoth in perspective we must learn of the other Outer Gods which it dwarves, Azathoth is seen as all-powerful yet is surpassed in strength by Yog-Sothoth and Yibb-Tstll is seen as all knowing yet is surpassed in knowledge by Yog-Sothoth: simply put Lovecraft heavily implied this being was the ultimate source of power in the cosmos.

Like many Lovecraftian deities Yog-Sothoth has a number of avatars and followers by which to expand its infernal influence and although classed as "evil" is technically an amoral character that is simply beyond our understanding of petty morality or sanity (indeed Lovecraft wrote in a very dark fashion that swayed away from moral absolutes and saw the universe as being cold and cruel by its very nature).