The classic rags-to-riches story got a macho spin in the Oscar-winning Rocky, which was written by its star, Sylvester Stallone, and began filming on this day in 1976. Stallone had his own rags-to-riches tale: Born in the gritty Hell’s Kitchen neighborhood of New York City, he was a juvenile delinquent who was kicked out of a number of schools before he turned 15. After attending high school in Philadelphia and studying drama at the University of Miami, Stallone moved back to New York and later to Los Angeles, with dreams of becoming an actor.

When the idea for Rocky came to him, Stallone was living in a seedy apartment in Hollywood with his wife and dog; he began writing scripts so that he would have better roles to play. According to a profile in the New York Times, published November 28, 1976, he wrote the entire Rocky script in a frenzied three and a half days. After a long negotiation process, Stallone sold the script to the producers Irwin Winkler and Robert Chartoff, on the condition that he play the lead character, the underdog boxer Rocky “The Italian Stallion” Balboa, himself. His only previous leading role was in the low-budget flop The Lords of Flatbush (1974), and the producers had wanted to cast an actor with a higher profile, such as James Caan, Burt Reynolds or Ryan O’Neal.

The inspiration for Rocky was a real-life fight between the world heavyweight champion Muhammad Ali and a little-known club fighter named Chuck Wepner. In March 1975, Wepner went 15 rounds against Ali in a title bout in Cleveland, Ohio; he had been such a big underdog before the fight that Sports Illustrated ran his picture on their cover with the headline “Boxing’s Strange Encounter.” In the movie, Rocky Balboa is a club fighter from Philadelphia who takes on the reigning world heavyweight champion, Apollo Creed (Carl Weathers), with the help of his trainer, Mickey (Burgess Meredith), and his love interest, Adrian (Talia Shire). Stallone trained six hours a day for five months to don Rocky’s boxing gloves, popping vitamins and hitting the gym to develop his 46-inch chest and 16-inch biceps.

Directed by John Avildsen and shot in 28 days on a $1 million budget, Rocky divided critics between raves and pans, but it became the sleeper hit of the year, making Stallone–who got 10 percent of the grosses–a rich man and a bona fide star. It was the first feature-length movie to employ the Steadicam, which was used primarily in the fight scenes and the scenes of Rocky running in Philadelphia during his training. Garrett Brown’s pioneering invention helped keep the moving camera steady to create a fluid, smooth shot. At the 1977 Academy Awards, Rocky was nominated in no fewer than 10 categories, including Best Actor and Best Original Screenplay, and won three Oscars: Best Director, Best Picture and Best Film Editing. It also spawned five sequels, including Rocky II-V over the course of the 1980s and Rocky Balboa (2006).