The Illuminati were a group of powerful individuals founded by the Stephen Strange of Earth-838 to protect their universe from high level threats, such as powerful beings and universe incursions.
The group initially consisted of Stephen Strange, Charles Xavier, Peggy Carter, Blackagar Boltagon, Maria Rambeau, and Reed Richards with Karl Mordo joining after Strange's death in the aftermath of the Battle of Titan. However, the group was later disbanded when all of its members except for Mordo were ruthlessly murdered by Wanda Maximoff.