Anybody who is anybody has seen Rocky and it's many sequels.
But did you know what or who was the inspiration behind the sports drama?
Why Sly did all the graft when it came to the actual screenplay, it was his dog Butkus who influenced Stallone to make the film that would go on to change his entire life for the better.
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In an Instagram post, the actor wrote: "1971... Since we're on the subject of 'man's best friend' this is myself and Butkus as a puppy, we were both, thin, hungry and living in a flophouse above a subway stop, I used to say this apartment had hot and cold running roaches.
"Anyway there was not much to do except spend time with each other and that's where I started to learn the craft of screenwriting. Since I never went out, I relied on his companionship.
"And actually it was his idea to write Rocky, but don't tell anyone...," Stallone revealed alongside the photograph of him and Butkus.
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The story then takes a turn for the tragic when Stallone opened up about how he was forced to sell his dog during a spell of poverty because he had no money to feed him.
Image: Instagram
"Years later when things got even worse I had to sell him for USD 40 in front of a 7-Eleven store, because I couldn't afford food," said Stallone.
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"Then like A modern day miracle, the screenplay for Rocky sold, and I could buy and buy him back, but the new owner knew I was desperate, and charged me USD 15,000 ... He was worth every penny!" Stallone added.
Today, Stallone's net worth is close to $400 million (£320 million), a far cry from his days as a struggling actor.
We mean, really struggling. Not 'a few rejections' struggling, but actual 'physically harmful' struggling.
Stallone in 1981. Image: PA
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He was so stuck for cash at one point that he reportedly stole his wife's jewelry to sell it. Before long, he was homeless and sleeping at a New York bus station.
Two weeks after selling his dog, he saw Mohammed Ali fight Chuck Wepner. It would serve as the inspiration behind his script for Rocky.
He was offered a whopping $100,000 for the screenplay but rejected it on the grounds that he had to be in the movie. It was a ballsy move for a homeless man.
Eventually, he walked away with just $25,000 (£20,000) because the production company wouldn't spend their money on someone they didn't trust. Stallone immediately went back to buy the dog.
Rocky would go on to be a worldwide hit, grossing $225 million (£180 million) worldwide and bagging the Best Picture Academy Award in 1977.
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He quickly produced two sequels for the Rocky Balboa character. In 1982, he introduced cinema-goers to a new character: the Vietnam vet John Rambo in First Blood. That itself would spawn many a sequel.
In the 90s, Stallone's presence as an action star faded with the release of films like Judge Dredd and Daylight in 1995 and 1996, respectively.
He eventually reprised his role as Rocky and Rambo in two films in the late noughties.
Returning full-time to the action-hero life, he starred alongside fellow tough-guys Bruce Willis and Arnold Schwarzenegger in The Expendables.
Featured Image Credit: InstagramTopics: Instagram, Sylvester Stallone, Rocky