Daniel Wiltshire suggests the interesting theory that the Warner Brothers cartoon character Rocky might have been based on the diminutive "B" Western star Bob Steele, whose best-known role in "A" movies was the tough guy Canino in The Big Sleep.
Personally I always thought Rocky and Mugsy were funnier characters to look at than to actually watch in action; their first cartoon with Bugs Bunny, "Bugs and Thugs," is an okay cartoon, but not a patch on Friz Freleng's earlier "Racketeer Rabbit," which does many of the same gags with gangsters who look like Edward G. Robinson and Peter Lorre. By the early '50s Warner Brothers had moved away from doing characters directly based on well-known movie stars and were going more for "timeless" characters who could be used repeatedly (and, perhaps, merchandised), but in many ways it was more fun to see Bugs or Daffy going up against characters based on the Great Gildersleeve or Humphrey Bogart -- direct, easily-identifiable pop-culture references, instead of vague similarities to a vaguely-familiar character actor. For some reason, direct pop-culture references seemed to vanish from WB cartoons around 1951 or '52, only to reappear again in the late '50s in the form of TV parodies; I've never quite figured out why.
Anyway, I think there's something to Daniel's theory; a lot of cartoon designs, and voices, are vaguely inspired by actors, and sometimes even people. On the other hand, since Steele's movies didn't make him look quite as short as he was, and since the WB animators might not have had first-hand knowledge of what he looked like offscreen (the WB animation studio was, until the early '50s, separate from the main WB lot, and the animators didn't see the live-action people very often), it's difficult to say whether Canino was the direct inspiration for Rocky.