Well, for starters, he's a horror/crime author. And if you'd like to know more, check the wikipedia entry for Brian Keene, or his official website.
How does this relate to Doom Patrol? Well, Keith Giffen recently revealed that Giffen himself will be the artist for #16, the designated "change-of-pace" issue. So who will be the writer? The following tidbit came from Brian Keene's website......
"As regular readers of Doom Patrol know, the legendary Keith Giffen has been writing the comic’s current incarnation. But he says here that he’s drawing issue #16. Very strange. If Keith is drawing issue #16, who is writing it? And in the same post, he asks people if they’ve heard of horror author Brian Keene. Why would he do that? He also tells Newsarama that #16 will be a “special change-of-pace” issue. Cryptic fellow, that Keith Giffen. Likes to call me up and say things like, “Men name their penises because they don’t want a total stranger making all their decisions for them…”
*I can’t confirm or deny anything."