The Grey Slayers were a Loyalist Space Marines Chapter of unknown origin and Founding that became corrupted by Chaos. Inquisitor Thrax purged the Chapter of mutants and daemons, and the Chapter Master took his own life in shame. Untainted officers were raised up to lead the Chapter. The purge was apparently not quite thorough enough, as Inquisitor Thrax himself was soon afterwards corrupted by the Ruinous Powers and transformed into some sort of daemonic Chaos beast. The Grey Slayers' eventual disposition and fate remains unknown in current Imperial records.