Grey Knights
The Grey Knights are a bunch of fucking badass SPESS MEHREENS that also, like their brethren, do it for the EMPRAH. The Grey Knights are the legendary 666th Spess mahreen chapter made by the Emprah and one of the few Chapters to have more than 1000 marines, they amount to 'bout...3000, beating out the Space Wolves who have 1440 marines but losing out to the Black Templars who have 6000-10000 marines, notably while the Grey Knights are an all psyker force, the Black Templars don't allow any psykers to join and both heavily draw from medieval influences, however it's almost certain that if all the Grey Knights were to fight all the Black Templars that the Black Templars would get squashed.
They're all made with the Gene-seed of the Emperor himself, making them sort of like mini-primarchs. The Grey Knights work under the Ordo Malleus and specialize in killing anything daemonic, so they're typically called in to deal with giant greater daemons of death or Chaos Primarchs themselves, and boy can they ruin any daemon's day. People outside the Ordo Malleus and high-lords of Terra do not know much about the Grey Knights, other than they exist and totally kick-ass, because their base of operations and anything that happens within their Chapter are never discussed outside the Ordo or by the High-lords though as the First war of Armageddon, Dawn of War:Dark Crusade, and Dawn of War:Soulstorm show, they'll work with other Chapters if the Ordo Malleus or one of their higher-ups decides that their presence is needed or if their presence is requested by the overall commander of Space Marine operations.
They don't necessarily have to fight Daemons and will readily deal with more mundane things like witches, mutants, and heretics which would normally be left to the Ordo Hereticus and their chamber militant the Sisters of Battle as well as their inquisitorial stormtroopers as well as Xenos which would normally be left to the Ordo Xenos and their chamber millitant the Deathwatch which is composed of the hardest non-grey knight space marines around as well as the usual inquisitorial stormtroopers; though the Grey Knights and their Ordo Malleus Inquisitorial Stormtrooper allies will typically feel that this is a waste of their talent.
All of this changes when Xeno Warp entities like the Avatars of Khaela Mensha Khaine and Enslavers appear or when said heretics, mutants, and witches bring out Daemons or some combination of the above, but this tends to end up causing two or if they're really unlucky; all three branches of the inquisition to descend down upon the poor sap. Fighting Inquisitorial Stormtroopers from all three branches, the Sisters of Battle, the Deathwatch, and the Grey Knights all at once is a challenge that most sapient entities would much rather slowly gnaw all of their legs off than face.
Grey Knights are also the most elite of the Space Marines and are trained in the most ball-crushingly hard process that even veteran space marines consider "hard". Unlike other marine chapters however, they're all Psykers and only induct Psykers as recruits from the inquisitorial "Black Ships", which collect Psykers throughout the Imperium for training. They're also the most pure of the Space Marine chapters, every last one of them thinks that Chaos is fucktarded and not a single Knight ever succumbed to Chaotic influences. Even a basic Grey Knight is capable of one shotting a lesser daemon with his force halberd in fluff terms, and a typical nameless Greater Daemon or Daemon prince can be sent shrieking back into the warp with one swing from a Grey Knight Grand Master. But for really big Daemonic threats like the Daemon Primarch Angron and An'ggrath, lots of Grey Knights will be needed to bring down the gribbly warp monster.
They are given the absolute best equipment the imperium can give, their basic troopers are nearly as well armed as most chapter's terminators, coming with a stormbolter and a force weapon vs a termies storm bolter and power weapon and they have access to the monstrously powerful Psycannon. However, they always prefer fighting at close combat where they can use their force weapons.
Table-top wise, Grey Knights are the optimum commando army, you're normally outnumbered but you are capable of tearing shit up if you lead your troops correctly. In an average 1,000 point match, you'll have 20 models and a land raider. But it's okay, because they kick ass. Plus all of their models subscribe to the Rule of Cool, they're more awesomesauce than regular marines and all their basic weapons are fuckawesome and their units all look really damned cool.
Though they are individually more powerful than the Deathwatch of the Ordo Xenos and are both more individually powerful and experienced than the Sisters of Battle of the Ordo Hereticus, they lack the experience and versatility of the Deathwatch who probably also outnumber them somewhat, and are vastly outnumbered by the Sisters of Battle, which keeps a balance of power between the three orders of the inquisition.
They also make fanatical faith in the God-Emprah cool:
"There is nothing in the arcane and blasphemous arsenal of the forces of Chaos that can compare to faith. With the power of faith, our weapons become shining instruments of deliverance that can cleave the mightiest daemon in twain. With the power of faith, our minds appear as slivers of pure agony to the daemon, driving into the wretched forms of those who would dare stand before us. With the power of faith, our words become commands that cause the daemon to cower and cringe in terror. I could meet my enemies unarmed without a shred of fear in my chest, for I know that the Emperor watches over me and guides my hand. So let them come. We shall show them what the power of faith can do."
+++ Captain Stern of the Grey Knights +++
TL;DR: Matt Ward wishes his Smurfs were this cool. So instead, he got his hands on their new codex and shat all over it.
See Also
- The 666 Rituals of Detestation - All Grey Knights initiates must pass these trials before they become a full-fledged battle brother.
- Daemonhunters