Shuma Gorath
(Also called He Who Sleeps But Who will Awaken)
The entity: Shuma-Gorath is 1 of the 3rd type of daemons, non-humanoid in form and alien in motivation. He (or rather it) is an enormous(50' diameter), brain-shaped, purple, tentacled, slug-like creature of vast power.
In the long forgotten eons of Earth, in those primal days of Earth's beginning, Shuma-Gorath was all. Spawned in a dimension diametrically opposed to Earth's he eventually made his way here and dominated. As the eons passed, Shuma-Gorath yearned for rest. Actually this was because a time travelling magician called Sise-neg, going back through time in an effort to drain all of the magical powers in the past and become God, drained Shuma-Gorath's powers, sent him to sleep, and sent him to another dimension. There he would dream and lie in wait until the time of his awakening.
It is said of Shuma-Gorath that "his power is his secret and his secret is his power." The secret was that his awareness rested in the mind of the Ancient One and that was how he planned on returning to power. Doctor Strange thwarted his plans by extinguishing the life of the Ancient One, thus dissipating Shuma-Gorath from this dimension. He still exists, and waits, for his chance to return.
The spells: Relatively unknown, except that he does have a number of lesser daemons and monsters who serve him and sometimes an evil character will call on Shuma-Gorath to grant him control over that creature, which he usually grants. Shuma-Gorath and his servant daemons also grant those who entreat them Eldritch Attack spells of Rm(30) to Am(50) spell ranks. His servants include Sligguth, Dagoth, N'Gabthoth, and Kathulos, the last 2 who are believed to be destroyed.