Sylvester Stallone wrote the screenplay for Rocky in three and a half days.

United Artists liked Stallone’s script and viewed it as a vehicle for a well-established star like Robert Redford, Ryan O’Neal, Burt Reynolds, or James Caan.

Although Chartoff and Irwin Winkler were enthusiastic about the script and the idea of Stallone playing the lead character, they were hesitant about having an unknown headline the film.

United Artist initially thought the project was going to be a disaster. Stallone’s agents insisted that Stallone portray the title character, to the point of issuing an ultimatum.

Stallone later said that he would never have forgiven himself had the film become a success with somebody else in the lead.He also knew that producers Irwin Winkler and Robert Chartoff’s contract with the studio enabled them to “greenlight” a project if the budget was kept low enough.

The producers also collateralized any possible losses with their big-budget entry, New York, New York (whose eventual losses were covered by Rocky’s success).