The Grey Knights are a Space Marines Chapter and the Chamber Militant for the Ordo Malleus. They specialize in the hunt and extermination of Chaos daemons.
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The Grey Knights are the legendary Chapter 666 – and although nominally a Chapter of the Astartes, they are in the Chamber Militant of the Inquisition. Each member of the chapter undergoes a grueling and torturous selection process, and even once inducted, their harsh training regime is without equal. In battle, they move as an army of silver ghosts, surrounded by awe, and equipped to the teeth to deal with the worst foes that Chaos can raise to meet them. Ever since the Chapter’s founding, only the Inquisition and Chapter Masters have been allowed to know of the Grey Knight’s existence.
Many chapters believe the Grey Knights to be a myth, if they have even heard of them at all. Space Marines who encounter them are telepathically scoured, while Imperial Guard regiments they fight beside are simply executed. The Space Wolves know of their existence however, after slaughtering Grey Knights, Red Hunters and Inquisition Forces, during what the Grey Knights call the Months of Shame.
To battle such enemies as Daemons, creatures that are not of this realm but formed of sorcery and madness, a Grey Knight must embrace the power of the Warp to battle a Daemon with its own weapons. Each Grey Knight is an accomplished, powerful psyker whose psychic presence is anathema to creatures of the Warp. They are trained to channel their psychic energies into a halo of protective wards known as The Aegis. Thusly armored, a Grey Knight’s presence becomes unpalatable to Daemons, making him immune to corruption, able to wield forbidden black magic, harness tainted artifacts and scour blasphemous tomes all without risk of being overwhelmed by the cursed power of Chaos. The Grey Knights hold a unique honor among the chapters of the Adeptus Astartes – in over ten thousand years of service, not a single one of their number has ever defected to Chaos.
Their armor is left unpainted, leaving the silver-grey of the ceramite exposed. This tradition is thought to have originated from their desire to lead lives of absolute purity. Acid-etched into their left gauntlet, as well as tattooed upon the flesh beneath, is the sigil of Malcador the Sigilite. Upon achieving the rank of Justicar one may display their personal heraldry on a shield on their shoulder. In contrast to this their armor is highly decorated, encrusted with protective symbols and engraved litanies.
The bulk of the Grey Knights Chapter is organized into Brotherhoods, fighting formations roughly equivalent to a Space Marine Company and consisting of around one hundred Battle Brothers. Each Brotherhood is overseen by a Grand Master There are eight known Grey Knights Brotherhoods plus the Purifier and Paladin Orders. Most of the Chapter’s strength is spread through the Imperium, ensuring that the fighting skills of the Grey Knights can be quickly called upon by the Ordo Malleus wherever a daemonic incursion may occur. These small forces are often stationed thousands of light years from their fortress-monastery for decades at a time, and are usually organised into small teams that have trained and fought together for their entire lives.