Gav Thorpe
The man responsible for totally destroying everything that Chaos stands for in Warhammer 40k. He went and fucked up the Chaos Space Marine codex.
Strangely, all other official materials written by Gav Thorpe don't seem to be nearly as screwed over. If the fucker EVER gets enough balls to put a gun in his mouth and pull the fucking trigger he would proably fuck it up. Edit: Oh hell, he just fucked over Nids as well.