Warhammer 40,000. Codex. Grey Knights

"The most mysterious of the Emperor's servants, the Grey Knights are a unique Chapter of Space Marines. Each is an elite warrior-mystic clad in sigil-scribed power armour and wielding archaic weapons through which they channel their otherworldly abilities. They are a purified order, incorruptible and possessed of iron fortitude. They have to be, for the Grey Knights face down the most nightmarish horrors from the seething depths of the warp: the Daemons of Chaos. Their Brotherhoods use the shifting immaterium to their advantage, drawing on it to direct coruscating energies and outmanoeuvring their foes through pinpoint teleportation. Their warriors unleash a storm of firepower, supported by sanctified battle tanks, gunships, and giant warsuits whose psychic weapons can banish the greatest of Daemons back into the warp."--Publisher's website.