Brotherhood Champion
A Brotherhood Champion is the Grey Knights' equivalent of a Company Champion seen among Space Marine Chapters.
While many Grey Knight Battle Brothers are skilled warriors, the Brotherhood Champion takes the cake as the ultimate fighter. These Marines forsake every other disciplines in favour of becoming extremely proficient swordsmen that can switch between two powerful stances. One being an offensive one, the other a defensive.
The main roles of such a Battle Brother is to act as a bodyguard to the Grand Master/Captain, and to meet and defeat powerful adversaries. In dire situations, the Champion will sacrifice himself to take his enemy with him as he dies, but these situations are really rare since there are very few warriors in the galaxy are that powerful (or lucky) that they can defeat a Brotherhood Champion in hand to hand combat. When he's about to pull something like that off, then his own suit literally reknits bone and flesh and temporarily resurrects the Champion so to allow him to strike at the one that killed him with lightning speed and catching said killer off guard (thus also avenging his own death). This shows how deadly and awesome these guys are. At this point, when the Champion finally dies, his soul goes beyond realspace and the body is recovered back to Titan so that the Champion would guard the ancient Vaults from evil even in death as he did in life.
When not in battle, a Brotherhood Champion will act as a drill instructor, training the new recruits and making them break a sweat.
Apart of the standard equipment used by Grey Knights, the Champion has a Iron Halo and a Nemesis Force Sword known as a Annointed Blade, which are a as old as the Chapter itself.
Of all the Brotherhood Champions, Castellan Crowe of The Purifiers is the deadliest and most powerful of them all (as well he holds a position as a Captain).