Castellan Garran Crowe is both Captain and Brotherhood Champion of the Purifiers of the Grey Knights Chapter of Space Marines. The Purifiers are a group of specialists that burn shit with their minds and are the purest-hearted of the Knights. Castellan Crowe, needless to say, is both of these things, as well as being one of the best swordsmen in the Grey Knights.
Sounds like a Mary Sue, no?
Ironically, Castellan Crowe is the only Grey Knights character (aside from Brother-Captain Stern) that has not earned the enmity of /tg/.
Y He No Part of Ward's Dick Club?
Because he's a badass.
He's a badass because he wields a daemon sword.
A daemon sword called the Black Blade of Antwyr.
A daemon sword that could not be destroyed by the Inquisition.
A daemon sword that mindfucked every other guy that had ever wielded it.
A daemon sword that corrupted three full sectors and required the entire Grey Knights Chapter to step in and stop it.
A daemon sword that actively tries to murder Crowe every time he wields it.
A daemon sword that has near-infinite power and might possibly be a God in its own right, just waiting to be unleashed...
But Crowe just uses it as a regular sword, because using that near-infinite power would corrupt him.
Also, barely enduring the influence of a single daemon weapon makes a lot more sense (and is a lot cooler than) not only surviving in the Warp, but actively destroying all the Chaos Gods' shit.
Although, Especially in the 5th edition book Ward makes sure to note how Crowe is the purest Marine of the purest purifier order of the purest space marines that are the Grey knights, so uhh, while a cool dude, even he is not safe from Ward taint.
7th Edition also adds and takes away from his sueness in equal measure by making the leader of the Purifier Order (where the purest of the pure are grouped) and making him the most likely guy to take the place of Kaldor Titanfucking Draigo, but he keeps refusing because he has a bigger job taking care of the extremely foul blade and trying to keep track of what it says so he might find that one golden nugget of truth amongst a sea of insults.