Purifier
Purifiers are those hard-as-balls devoted Grey Knights who are so pure that their pureness radiates extra purity that burns Daemons if they get too close. Despite their Mary Sue description, Purifiers are commended for giving birth to one of the few genuinely badass Grey Knights after the fiasco of Ward. How they haven't become Living Saints yet is a source of mystery. They form one of two elite brotherhoods and are distinguishable by their white painted helmets, the others being the Paladins.
Membership in their number is given to those that show a tally of grim deeds soaked in blood, valour and skill, with no set procedure or training regime for entering their ranks. In fact, a Grey Knight can serve the Chapter for centuries with distinction without ever being granted the honour of membership into the Brotherhood of Purifiers. The Purifiers themselves only select those Battle-Brothers who show an incorruptible soul and who demonstrate resistance to the temptations of the Warp even amongst the standards of the Grey Knights.
This high standard meant that there are only a few Purifiers at any time, and no thought has ever been given to relaxing the restrictions, in fear that it would compromise the sanctity of their order. At any given moment, there are rarely more than forty Purifiers and only with the arrival of some great incursion do their ranks swell in number. Fortunately, even their limited numbers prove adequate to the task and they often ensure their sacred duty of combating the machinations of Daemons thus allowing the fires of victory to endure. This duty means that they often form the spearhead of any assault, though, as is the case with all Grey Knights, they understand that their mission comes first before personal survival.
Purifiers being elites to the elites of the elites are given extremely powerful Daemon-munching weapons. This includes a Wrist-mounted Storm Bolter, Nemesis Force Sword, Frag Grenades, Krak Grenades and Psyk-Out Grenades. Purifiers are also able to channel certain psychic abilities such as Cleansing Flame which allows them to call upon their purity, psychic gifts, and fanatical devotion to duty to create a nimbus of flame around themselves that burns all nearby enemies with white hot soul fire. When this power is manifested the Purifier bursts with white light and is momentarily surrounded by a corona of consecrated flame. The Purifiers then send forth the pure fire in their souls to consume their foes. The other psychic ability is Hammerhand which is essentially crushes the opponent via their mind akin to the Force from Star Wars.