Is not Christian Dunn. He is Alex Stewart, however, who wrote those Dark Heresy books you nerd rage about. Sandy is not a girl's name (Spongebob was lying to you). Alex is. He writes the Ciaphas Cain novels. He also did some Warhammer Fantasy books which were pretty good.
Went on a bit of writing hiatus after about three omnibus' worth of Cain books, not producing anything for three years to everyone's great sadness, and for a while, it seemed like he didn't work at the Black Library anymore. However, it's recently been revealed that he is working on a new Cain book right now. We'd certainly all like to see how Cain reacts to Guilliman getting back up.
...which is too bad, because the Cain books all take place before Guilliman gets off his ass.
- While Abnett and McNeill are part of the trinity by virtue of writing awesome, by contrast Mitchell is part of the trinity by virtue of being fun. Yeah, remember "Fun"? The whole reason you got into the wargaming hobby in the first place? Yeah, yeah, fun is not very Grimdark, but you need a little fun to enjoy the Grimdark, because if there was none to be had it would be too depressing to play. Humor is, after all, a natural coping mechanism to tragedy and horror, and Mitchell plays that to a hilt. He is not afraid to take the piss out of the setting on occasion, and throws in a few referential jokes and plays on language for amusement.
- Is fond of quirky characters who challenge their stereotypical depiction in the setting, yet still fit into it and avoid the trap of falling into burlesque caricatures: a cowardly commissar, a perky Inquisitor, a guardsman who prefers a chain-axe as weapon, a disgustingly filthy guardsman secretary, a Sister Superior who has a discreet sexual relationship, and a Chaos Lord who leads through a mix of fiery speeches and psychic powers while sporting a Hitler moustache. Where else are you going to find gold like that in 40K canon?
- Actually manages to describe the worlds of the Imperium as places which actually don't suck so hard to live in, without making them sound like straight up utopias. Through the eyes of Cain, you find that many of them are not that different from today's Earth, and people there can actually live their lives quite happily (as long as shit isn't hitting the fan, that is).
- Seems to have a thing about the Necrons being the most deadly dangerous damn things in all of creation (akin to the Borg in TNG era Star Trek). Out of all the enemies that Cain has faced, he is particularly terrified of the Necrons, to the point of almost having panic attacks at the mere memory of them. Cain fights enemies like Orks, Chaos, and even Tyranids on a fairly consistent basis, but when the ‘Crons show up there always seems to be virtually nothing that can be done about them short of overkill on a near-planetary scale.
- Known to troll his fanbase. You would think a book named The Greater Good with a Tau and a Commissar fighting Tyranids back-to-back together on the cover would be an awesome team-up between the Imperium of Man and the Tau Empire, right? Wrong, both parties declare a ceasefire and go to defend their own domains while trying to spy on the other and/or diverting the 'nids the other's way. Problem, fanboys?
- Hates Pyrovores. **SSSSS Crudface'sssss terrible heavy flamer equivalent hasssss been reeeeemade for the swaaaaarm's proper use... And Ripperrrrrs have been dissssspatched to infest his bedsheeeeets...**
- Apparently doesn't think much of the Eldar/Aeldari name change. While his most recent work does include changes like the Astra Militarum and T'au, Eldar conspicuously remain Eldar, with Cain and his associates (even Amberley) seemingly oblivious to any more "proper" name for them. You can't say this was simply an oversight or written before the name change either, because when Cain comes up with the word "Eldary," it's mocked quite pointedly.