Growing up alongside fellow Falcone gang member Jimmy Saviano, Gilzean and Saviano were delinquents at an early age. One time, the pair robbed a butcher shop, stealing several pounds of meat for their families. Despite a brotherly relationship, Butch withheld several prime cuts from Saviano, leaving his partner-in-crime clueless that he had received the inferior ground beef. Disappointed with his choice later on, Gilzean kept his decision a secret for many years. 
Butch is a jovially brutal individual, happy to hand over the baseball bat to Oswald and encourage him to continue the beating others started. He appears to like Harvey Bullock on a personal level, but shares Fish's ability to truly believe that 'it's only business' when he hangs the cop up and leaves him to be filleted. Butch is the sole survivor, from his group, of the cop killing attempt, and suitably submissive to Don Falcone, which probably explains why he's still breathing at the end of the episode. The other examples of Fish Mooney's henchmen are not so fortunate. He has a contempt for cops which his profession generally requires him to mask, but when ordered to take out James Gordon and Bullock, he does so with a certain relish.
Butch was later brainwashed by Victor Zsasz, in order for him to work for Oswald Cobblepot. During the events of the Falcone-Maroni Gang War, Butch accompanies Cobblepot when he attempts to kill Falcone in the hospital, but are stopped by Gordon. Gordon and Bullock take Falcone, Cobblepot and Butch to one of his safehouses, but Fish Mooney and her gang ambush them. Butch is then recruited back to Fish's crew but he is struggling to stand beside her since he is still under Cobblepot's control. After Fish kills Maroni and recaptures Falcone, Bullock and Gordon who try to escape Cobblepot comes in and shoots the majority of Fish's crew and chases her up to the roof. With Fish and Cobblepot struggling for who gets to control Gotham, Butch arrives holding the two at gunpoint, since his mind is still struggling to choose a side, Butch shoots both Fish and Cobblepot. After realizes what he had just done Butch rushes to his friend and apologizes for what he has done, Fish forgives him and assures him she'll be fine, but before either could react, Cobblepot knocks Butch down and pushes Fish gaining complete control of Gotham and with Butch now completely at his mercy. Cobblepot later cuts off his hand, so he can go under cover to rescue his mother from Theodore Galavan. His hand was later replaced with a mallet.
- Butch Gilzean is portrayed by Drew Powell.
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