King in Yellow
Believed by some to be a figure of mere folk legend, the legend of the King and his inner circle known as The Eight have existed for many centuries. He is an enemy of both Gregor Eisenhorn and Gideon Ravenor as well as rival Chaos Space Marine sects. The King's identity and purpose are unknown, except that it involves the Immaterium. Apparently, one of his goals is to obtain the true name of the Emperor in order to obtain power over Him, and this has led him in searches from the Planet of the Sorcerers to Sicarius to the Black Library. Eisenhorn has pledged to hunt down and destroy the King before he completes his ultimate objective.
In the works of H.P. Lovecraft the King in Yellow is a mysterious bringer of doom and madness associated with the play of the same name.