Robert "Rocky" Balboa was the only child of a Roman Catholic Italian-American family. He never graduated high school, and his father told him he wasn't born with much brain, so he had better use his body. This encouraged him to take up boxing. He trained very hard so he could grow up to be like his idol Rocky Marciano. His nickname is "The Italian Stallion," spawning from his Italian-American heritage.
A well-known boxing champion, Rocky enlisted in the military in a secret posting with the G.I. Joe Team. He was specifically recruited by Hawk in order to train the Joes in pugilism and "how to take a beating." It is said that no one could touch him, even with pugil sticks.
The Herb Trimpe artwork in Order of Battle #2 was not drawn with Sylvester Stallone's likeness, since the deal was not yet official. In addition to appearing inside the issue, Rocky appears on the back half of the wraparound cover, near Rock 'n Roll, Short-Fuze, and Slaughter's Renegades. Rocky's appearance was retracted in Order of Battle #3 and #4, and removed entirely in the trade paperback. Thus, he no longer exists in G.I. Joe continuity. It is likely that the character art's lack of resemblance to Stallone is why Marvel only had to run retractions, not recall and destroy the issues, since only the name was an infringement.