The Grey Knights are a Loyalist Space Marine Chapter, created by the Emperor of Mankind during the Great Crusade to serve as the Imperium's instrument of war against the forces of Chaos. They are a unique Chapter, tasked with hunting down and destroying Chaos cults, Daemonic entities, and other threats to humanity.
The Grey Knights were formed from the stock of the Emperor's most trusted Space Marines, who were chosen for their unwavering loyalty and unshakeable resolve. They are led by the Grand Master, who is the supreme commander of the Chapter.