Did Gambol (played by Michael Jai White) appear in the comics either before or after the Dark Knight movie?
He is a made up villain in the Nolanverse to fill out the demographic for a variety of organized crime families.
Taken from an interview with White by The Hollywood Reporter:
Nolan offered White the role of Gambol — the no-nonsense gangster who signed his own death warrant when he tried to tangle with The Joker, brought to life by Ledger in an Oscar-winning performance.
While never a principal role, Gambol was bigger in the script and during production, White says.
"It was the kind of thing where they had deeper intentions for Gambol; it was a character who was written for future use, I think," he says. "There were other plans to do stuff with that character and some things that were cut out. I think it's because of unfortunately losing Heath Ledger."
Calling it a matter of "tying up loose ends," White says he got why Nolan made the choice in postproduction.
Seems Nolan had more plans for the character but they never happened, this coupled with the fact this character does not appear to my knowledge in any Batman comic or cartoon before this suggests he is a Nolan invention