Animator Friz Freleng enjoyed creating new adversaries for Warners' star Bugs Bunny, since he felt that Bugs' other nemeses, such as Elmer Fudd and Beaky Buzzard, were too stupid to give the rabbit any real challenge. Freleng introduced two of these more formidable opponents as a pair of gangsters in the 1946 film "Racketeer Rabbit". In the film, Bugs decides to find himself a new home, but the one he chooses is unfortunately occupied by a duo of bank robbers. The characters here are called "Rocky" (drawn like movie gangster Edward G. Robinson) and "Hugo" (a caricatured Peter Lorre). Both gangsters are performed by voice actor Mel Blanc.
Freleng liked the mobster idea, and he used the concept again in the 1950 short "Golden Yeggs". This time it's Porky Pig and Daffy Duck who run afoul of the Mob, only this time Rocky has not only one sidekick, but an entire gang. Freleng also redesigned Rocky for this short, making him a more generalized caricature of the "tough guy" gangster rather than Robinson in particular. Freleng used several of the same techniques that would make his other Bugs villain, Yosemite Sam, such a humorous character: despite Rocky's tough-guy demeanor, everlasting cigar and foppish gangster dress, he's little more than a dwarf in a much-too-large hat.
In 1953's "Catty Cornered", Freleng set the Mob against another of his comic duos, Tweety Bird and Sylvester. Gang leader Rocky, this time aided and abetted by a hulking simpleton named "Nick", kidnaps Tweety Bird, and when Sylvester's bumbling predations accidentally free the bird, the poor puss is hailed as a hero. The duo reappear in 1954's "Bugs and Thugs", this time in the form Freleng would keep them for the rest of their run. "Nick" is here rechristened "Mugsy", and though his over-muscled body stays mostly the same, his hair is gone, and his facial expressions are decidedly less intelligent. Rocky and Mugsy would appear in two more Freleng cartoons: "Bugsy and Mugsy" (1957) and "The Unmentionables" (1963). Mugsy also appears without his boss in a cameo as one of Napoleon's guards in the 1956 Freleng short "Napoleon Bunny-Part".
Rocky and Mugsy have also appeared in various Looney Tunes-related merchandise. They are semi-regular characters in Looney Tunes comic books, for example. They also play the villains in the 2002 XBox video game Loons: The Fight for Fame, a first-person shooter in which the no-good gangsters attempt to run a film studio into the ground so they can buy up the stock for next to nothing.