Robert Thorne

Robert Thorne is "the biggest New York gangster leader," according to Batman. He seems to really hate Two-Face, as he orders Batman and Robin (A.K.A. the undercover thugs Bob and John Smith) to kill him. According to his debut appearance in the episode Going Undercover, he must be a dangerous guy after Batman and Robin went undercover for two months just to kill him (however the whole episode would later be revealed as Batman's "better plan" to stop the criminal). Despite being a villian, he hasn't made reappearances except for cameos in the Lego Batman Youtube Series.

Trivia

 * It is most likely that Robert Thorne is a one-shot villianous character who never majorly reappeared again after he was shot by Batman and Robin.