He was the lead designer on the original Necromunda, Epic and Battlefleet Gothic, and he also wrote a lot of balanced codices. One of the more famous ones was 3rd edition Codex Orks. Although the codices were a master piece of character, fun and balance, the wording of the rules was shoddy, ambiguous, contradictory and even missing at times. Also wrote for White Dwarf a lot, usually under the subtitle "Chambers of the Horned Rat".
Lately, he's been working for Hawk Wargames on Dropfleet Commander. It's also been recently revealed that he will be writing the story for the upcoming Necromunda Vidya gaem, in a pseudo return to his roots.