Previously, he'd worked for a company called Relic Entertainment, and was the lead designer on Dawn of War, a Warhammer 40000 (Warhammer, but in the future, kind of like Starcraft to our Warcraft)-based RTS game. The good news is that the game was fairly well reviewed, but of course Diablo 3 isn't an RTS game, it's a hack-and-slash, so we're not sure how Wilson will do on that front yet.
In this interview, Wilson was known to be at Blizzard and supposedly working on Starcraft II but of course now we know better. This new Diablo could be the chance for this developer new to Blizzard to claim his place in history.
UPDATE: Our very own Joystiq caught up with Jay Wilson at the Blizzard Worldwide Invitational. Find out what Diablo 3's lead designer has to say about porting to consoles, the next Deckard Cain rap and the notorious dupe exploits of previous games.