Tommy Flanagan himself confirmed that he'd joined the cast of Gotham early last month with the below Tweet, but now Comicbook.com has found out which character he'll be playing: it seems Mr. Flanagan will be bringing life to yet another villain, as he'll appear as a vicious but charming contract killer named The Knife.
Here's the site's description of The Knife, who would seem to be a character created just for the show. "The Knife is one of Gotham’s most dangerous denizens. His charming, stylish shell and good humor mask a remorseless hitman whose skills are at the service of the highest bidder. He will sit with you, laugh with you, and then cut your throat."
Apparently Flanagan will make his debut in episode 10 of Gotham, which continues tonight.