Chairman and former owner of Games Workshop. How bad is he? Forbes magazine allegedly described him as a "fucking tosser," which for those unfamiliar is akin to being called an unpleasantly diseased scrotum by Nurgle, or being asked to control one's temper by Angron.
He continues GW's quest to make Warhammer as unplayable as possible and be as much of a dick to the devoted fanbase as possible. His reward thus far has been a company rapidly trending downward towards dissolution and irrelevance, or at least that's what people have been saying since about 1993. There's a recurring theme of the media calling him a straight-talking person followed by him giving nothing but vague and/or evasive replies when he speaks, making it some kind of media in-joke.
Update: As of January 1st, 2015, Tom Kirby will be stepping down as CEO of Games Workshop. The company's board of directors has decided to use Tom Kirby's "we recruit for attitude and not for skill" logic in order to find their next CEO, thus anyone interested in the position merely needs to apply for it. This likely entails the coming of a sea of rage and butthurt, as thousands of neckbeards are denied an interview. (Probably correctly, since he is presumably looking for people with GOOD attitudes, not rage-filled snowflakes.) If a suitable candidate cannot be found, Tom Kirby's wife will probably take his seat as CEO. Yeah.
The new CEO is named Kevin Rountree, who used to be their COO, and before that, their CFO (and before that, middle management).
Bottom line, Tom Kirby is a typical douchenozzle, next financial quarter thinker type, in an industry that thrives first on genuine creativity and imagination. He only cares about leeching the phenomenon the great Ian Livingstone created.
He is now basically gone, stepping down after GW released their 2016-17 financial reports that showed massive profit increases under Rountree. He'll remain a consultant for 12 months before being replaced.