Grey Knights

Citadel of Titan — The Terminus Decree & Chamber of Purity

Designated Chapter 666 despite being founded at the very end of the Horus Heresy before the Second Founding even began, the Grey Knights are the Chamber Militant of the Ordo Malleus. During the Siege of Terra, Malcador the Sigillite hid Saturn's largest moon, Titan—pre-stocked with fortresses, gene-vaults, and a thousand hand-picked psykers alongside eight Founding Grand Masters drawn from both Loyalist and Traitor Legions—inside a time-dilated pocket of the Warp, so that when Titan re-emerged after the Heresy, a fully trained Chapter of incorruptible Daemonhunters stood ready.

Unlike any other Chapter, the Grey Knights' gene-seed does not come from a Primarch: it is derived from the Emperor's own flesh and blood ('The Emperor's Gift'). Every single Grey Knight is a potent psyker whose mind is fused with his squadmates in the 'Aegis' gestalt, and not one brother has ever fallen to Chaos in ten thousand years.

Sub-Factions, Secret Orders & Classified Relics

• The Eight Original Grand Masters — Janus (Revuel Arvida of the Thousand Sons fused with a shard of Magnus), Epimetheus (a Dark Angel buried in stasis on Pandorax), Koios, Khyron, Iapto, Yotun, Ogen, and Satre.
• The Order of Purifiers (Garran Crowe's Wardens) — Forty incorruptible warriors who guard the 'Chamber of Purity' beneath Titan where the talking daemon-blade of Antwyr and hundreds of indestructible Chaos relics are locked.
• The Ferrymen (Moritat-Seneschals of the Dead) — Former Grey Knights who have magically become Psychic Blanks (Pariahs) to tend the subterranean Crypts of Titan where fallen Grand Masters rest.