Sylvester Stallone was not born to be a star — which made him the perfect choice to play the titular Rocky Balboa in his breakthrough 1976 film, Rocky.

Prior to making his Oscar-winning blockbuster, Stallone spent years roughing it as a no-name actor in New York, appearing in a handful of low-profile films throughout the early '70s (including the 1970 softcore pornographic film The Party at Kitty and Stud's, which he later called "horrendous"). He first earned critical acclaim by starring alongside Perry King and Henry Winkler in 1974's The Lords of Flatbush, a low-budget drama following four teenage, leather jacket-wearing miscreants around the streets of Brooklyn.

Stallone also moved in 1974 to Hollywood, where he continued seeking acting work to little avail. His life changed on March 24, 1975, when he watched boxer Chuck Wepner — also known as the "The Bayonne Bleeder" — fight world heavyweight champion Muhammad Ali. Wepner was all but guaranteed to lose the match, yet he stood his ground against Ali and made it to the 15th and final round, when Ali knocked him out. At one point, Wepner also knocked Ali down, becoming one of only four fighters in history to drop the champ.

"I saw a man they called 'The Bayonne Bleeder,’ who didn’t have a chance at all, against the greatest fighting machine, supposedly, that ever lived," Stallone recalled in The Rocky Story. "And for one brief moment, this supposed stumblebum turned out to be magnificent. And the fact that he lasted and knocked the champion down... I said, 'Boy, if this isn’t a metaphor for life.'"

The Ali vs. Wepner fight served as the catalyst for the Rocky script, about a down-on-his-luck, past-his-prime boxer who is plucked out of obscurity and given a shot at the heavyweight title against reigning champion Apollo Creed (Carl Weathers). Along the way, Rocky falls in love with Adrian Pennino (Talia Shire), the sister of his best friend, Paulie (Burt Young), and fulfills his quest for self-actualization.

Watch the 'Rocky' Trailer

Stallone wrote the initial script in three days, although he estimated that "maybe 10%" of his first draft made it to film. To fit the cinematic trends of the time, he initially wrote Rocky as a gritty antihero, while his coach, Mickey Goldmill (Burgess Meredith), was a racist man with an even worse temper than what later appeared onscreen. Stallone originally planned for Rocky to throw the fight against Apollo because he no longer wanted to be part of the sleazy underworld of professional boxing. But his then-wife, Sasha Czack, didn't like the direction, and Stallone eventually rewrote the script to resemble the version that made it to theaters.

At a casting call, Stallone offhandedly mentioned his script to the producers, who told him to bring it by later. United Artists loved the script and wanted to finance Rocky, with one caveat: Stallone couldn't play the protagonist. They company wanted a proper movie star like Robert Redford, Burt Reynolds or James Caan to lead the film, and offered Stallone — who at the time had $106 in his bank account — over $300,000 for the script.

Still, the actor stuck to his guns. "I thought, 'Alright, you've really managed poverty very well. You've got this down to a science. You really don't need much to live on,'" he said. "So I thought, 'You know what? I know in the back of my mind if I sell this script and it does very, very well, I'm gonna jump off a building if I'm not in it.' There’s no doubt about it. I’m gonna leap in front of a train. I’m gonna be very upset. So this is one of those things where you just roll the dice, and you fly by the proverbial seat of your pants and say, ‘Alright, I gotta try it. I gotta just do it. I may be totally wrong, and I’m gonna be taking a lot of people down with me, but I just believe in it.’”

Producers Irwin Winkler and Robert Chartoff eventually got Rocky greenlit with Stallone in the lead role. With a meager budget of just over $1 million, Stallone and director John G. Avildsen hit the streets of Philadelphia in a van, using Garrett Brown's newly invented Steadicam to get smooth shots of Rocky running through the city. "Finally my legs basically gave out, and I'm writhing on the ground, and I want to rise up and say, 'John, I'm dying here,'" Stallone recalled. "And he goes, 'Use it! Use the pain.'"

Other training scenes were similarly excruciating, including the famous scene of Rocky punching slabs of beef in the meat locker where Paulie works. "I don't know if anyone's hit a bull lately. They're hard, they're real hard," Stallone said. "So my knuckles are flattened out. ... I don’t know what they’re good for anymore, I guess kind of like a table leg now. They’re pretty flat, they’re pretty even, they really don’t function as a hand much anymore."

Watch the 'Rocky' Training Montage

Stallone cut costs by casting his father, Frank Stallone, as a bellringer, and his brother, Frank Stallone Jr., as a street corner singer. His wife, Sasha, also served as the on-set photographer. Two other last-minute casting decisions would also shape Rocky: Shire as Adrian and Weathers as Apollo Creed.

"We just read, and I felt the earth move," Stallone said of Shire's audition. "I really felt a tremendous vitality and kinship. I loved her." As filming progressed, it dawned on Stallone that Rocky's relationship with Adrian would define the film. "These two people are two halves that absolutely need to fit together," he continued. “And I’m starting to realize that this is the key to the film. This is the heartbeat. The whole movie is going to be based on the discovery of these two people, the love.”

Weathers, meanwhile, brought the same snappiness and swagger to the set that Apollo Creed brought to the ring. Stallone knew he was the right man for the job as soon as they started reading lines and boxing, with Weathers landing several stinging blows on Stallone during his audition. "Then he sits back down and he goes, 'Mr. Avildsen, I could do much better if you had a real actor reading with me,'" Stallone recalled. "He goes, 'Well, Carl, that's Rocky. That's the guy who wrote the script.' He goes, 'Maybe he'll get better.'"

Stallone originally wrote a subdued, melancholy ending for Rocky in which he meandered through the post-fight crowd looking for Adrian, and the couple walked silently toward the locker room, “being anonymous forevermore.” But it didn't sit right with Stallone: "We thought, ‘Boy, wouldn’t it be interesting to catch a man’s life at the quintessential, seminal moment?'"

Stallone rewrote the final scene to show Adrian running into the ring, where she and Rocky exchange "I love you's" and the film fades to black on a freeze-frame of the fighter's bruised, ecstatic face. "We all hit this absolute maximum of elation and celebration that can only be sustained for an infinitesimal moment in time," Stallone said. "And that’s how we froze the original Rocky. He went out at the height. His life will never be more rewarding or more important or more valid than that second.”

Rocky Balboa Vs. Apollo Creed

That wasn't entirely true — for either Rocky or Stallone. Rocky became a sleeper hit upon its release on Nov. 21, 1976, earning more than $225 million globally (over $1 billion adjusted for inflation) and becoming the highest-grossing film of the year. It received 10 Academy Award nominations and won three, beating out NetworkTaxi DriverAll the President's Men and Bound for Glory for Best Picture. Rocky spawned multiple sequels and the successful Creed spinoff series, turning Stallone into a household name. He would go on to star in the Rambo franchise and several other lucrative (albeit critically panned) action flicks, including CobraTango & Cash and Cliffhanger.

Still, Stallone's proudest career moment came when Rocky was shown at the Director's Guild of America. The jokes weren't landing with the crowd; the fight scenes provoked no response. Stallone thought his film had bombed. But as he and his mother left the theater, hundreds of moviegoers crowded at the bottom of the stairs burst into applause.

"I just completely came apart. So there will never be a moment like that, ever," Stallone recalled. "When you find the right components in your life, the right people that gel with you, then you feel as though you’re invincible. It may be a fallacy, but you at least feel as though you can take all that life has to dish out."

'Rocky' Films Ranked

Much like the fictional fighter’s life, the Rocky films have experienced both highs and lows. We've ranked them all from worst to best.

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