Matthew Farrer
"I’ve been a fan of Matt’s work since I first read it, and I think his Enforcer trilogy featuring the Adeptus Arbites Shira Lucina Calpurnia is entirely made out of epic win with a splash of awesome sauce."
- – Dan Abnett. (Really.)
A seriously underrated author for Black Library, Matthew Farrer happens to be one of the few authors who does not live in the UK - in this case, he is from the land down under. Farrer's mostly relegated to more obscure stuff and hasn't done a novel length work for them for a while; Also writes a bunch of short stories that wind up in anthologies, including some Eldar stuff, Sabbat Worlds and Iron Hands as well as some short Warhammer Fantasy works.
He did the Shira Calpurnia novels, one of the few works with the Adeptus Arbites as the main characters, and are pretty good reads at that; the first, Crossfire, is probably the best of the bunch, as a detective procedural/thriller against the backdrop of the grim darkness of the 41st millenium. The last of the trilogy, Blind, also provides a rare glimpse into the details of the lives of Imperial astropaths.
Farrer also wrote a really good Necromunda story called Junktion, which is practically a standalone work with little connection to what we see as 40k at large (not a single mention of the Emprah or his Spess Mehreens, or Xenos, or the Inquisition, or Chaos, or...); naturally, this about fits for people who live out their whole lives in the forgotten holes of the Underhive.
Matthew Farrer contributed greatly to our perception of Angron through the story After De'shea, basically defining the at-least-slightly-sympathetic modern perspective on the character - a man with noble traits but seriously fucked over by unending grim darkness, ranging from the Butcher's Nails to the seeming utter lack of pathos from the Emperor.
His short story The Memory of Flesh, about some post-Heresy Iron Hands fighting some obscure xenos with the ability to affect the nervous system of their enemies, is perhaps one of the most potent portrayals in 40k that displays how grimdark the whole concept of Servitors, used by the putative good guys, actually is, not to mention it provides general insight into the psyche (psychopathology?) of that most-underdeveloped Loyalist chapter.
He is not Steve Lyons.