Don't bother going to your mind palace to see if you can remember who Butch Gilzean is from DC's comics, or searching Wikipedia. He's a new character created for Fox's Gotham, and Deadline is reporting Drew Powell will play him in the upcoming series. Powell is probably best known for starring in television's Ponderosa, and his guest roles in Malcolm in the Middle, Leverage, True Blood and Bones. He also appeared in Southland with Ben McKenzie, who will be playing Detective Jim Gordon in Fox's new series.
So who is Butch Gilzean? He's "the deceptively clever and ambitious second-in-command to sadistic gangster boss Fish Mooney (Jada Pinkett-Smith)." But the character won't play a huge part in Gotham: Deadline says it'll only be a guest starring/recurring role.
I've liked everything I've heard about the new series so far (except for the crappy dialogue from the possible spoilers), and Fox has cast some very solid actors in their show, including Robert Lord Taylor as The Penguin and Sean Pertwee as Alfred Pennyworth. There are a bunch of television series based on comics heading to the small screen soon, but Gotham is definitely the one I'm the most interested in seeing.
Gotham is scheduled to start filming in April, and could potentially debut on Fox this fall.