The Seven Stars
This being was an illithid created from the host body of a man named Strom Wakeman, the author of The Illithiad.
Wakeman, an enterprising trader and scholar of Underdark exotica, allowed himself to be captured by the illithids on one of his expeditions. Through the use of a non-magical mixture of various herbs that Wakeman named laethen, he was able to preserve his consciousness through ceremorphosis, and learned to use his psionic powers to keep from having to consume brains. Thus he worked against the illithid plots from within. The legend of the Adversary was born from his frequent sabotage, though the actual acts were never connected to him. The Seven Stars became his agents in stopping the illithids’ plans, as his own movements rely upon secrecy from his “fellow” illithids.
For another person to imitate Wakeman’s deed would require at least one dose of laethen (the making of which Wakeman kept secret) and to be put under ceremorphosis within a week of consumption. The drug only has a 40% chance of success, and the new illithid must also never consume a brain, for the act destroys the host’s personality and replaces it with the illithid personality.