The Sleeper

The Sleeper was the name of a dangerous and highly destructive evil that slept within Outhria for generations. It wasn't seen until the Third Old One War, where it was defeated by the Old Ones and seemingly finished off by Jadus with his "god blade". However, it is stated that The Sleeper remains alive, hiding in a dimension.
==Abilities and Powers==
The Sleeper was able to fight off all ten of the Old Ones, separately or together. It could summon large amounts of eldritch beings that could stand against them, and its blood even gave birth to these beings. In addition, it could breathe dangerous and volatile matter, and destroy multiple areas at once. 
==Speculation==
The Sleeper is believed to have been the entity that gave Grimmok and O.M.N.I. their powers that resulted in the Maelstrom War and the Great Turnback.