The Illuminati was a secret organization comprised of several of the world's most powerful heroes: Sorceror Supreme Doctor Strange; Black Bolt, King of the Inhumans; Charles Xavier, founder of the X-Men and mutant rights activist; Reed Richards, founding member of the Fantastic Four; Namor the Sub-Mariner, King of Atlantis; and Iron Man (Anthony Stark), founding member of the Avengers. These six men have worked together for an unspecified amount of time to mold and shape the status of the superhuman world and the world around it.
Originally, Tony Stark united these men along with the Black Panther shortly after the Kree-Skrull War had first involved Earth. He suggested they form a mega group that would be prepared to face such similar threats by uniting all of the existing super teams and groups. Eventually, the idea was minimized in scale to a secret cabal that would share information and decide secretly how all of the individual groups would correspond, with T'challa choosing not to join the group.
The group met to discuss a variety of issues, including the return of the Sentry. The group lasted until Iron Man decided to trick the Hulk into going into space, then sending him off from Earth to a distant planet. With Namor leaving because of his disagreement with the choice and Professor Xavier having disappeared after the Scarlet Witch warped reality, the group disassembled. They came together once after, when Iron Man announced the impending Super Human Registration Act, and asked that they all strongly agree in public in order to prevent a civil war. Again, the group was divided, and the Illuminati was permanently ended.
Members:
Iron Man
Mister Fantastic
Doctor Strange
Black Bolt
Professor X
The Sub-Mariner