Sylvester Stallone's life is the Rocky Balboa story

Director Peter Farrelly says Sylvester Stallone's life is the real Rocky Balboa story.

Farrelly's film - I Play Rocky - which brings to the big screen the story behind the making of Rocky, had its premiere at the Toronto International Film Festival on Saturday.

Stallone wrote and starred in the 1976 film - an underdog story that became a cultural phenomenon and inspired many fans of Stallone's fictional character Rocky Balboa's sheer determination.

Farrelly aims to present I Play Rocky to fans of the fictional Philadelphia boxer, and to a new, younger crowd unfamiliar with Stallone's struggles before he became the star of Rocky.

"The Rocky story is actually a true story. Rocky is fiction, but Stallone's story is the Rocky story," Farrelly said.

"And the message is: you never give up and you never give in. You can't be bought out. And in this day and age, everybody's bought out, everybody goes for the money. He didn't."

Asked if Stallone had watched the movie yet, Farrelly said the 80-year-old watched it alone.

"It was nerve-wracking because he (Stallone) saw it alone. And this is a great movie with a crowd. I didn't know how he was going to take it," Farrelly said.

Stallone was an obscure actor before pitching the story and stubbornly refused to let studios cast anyone but him in the role.

Anthony Ippolito plays Stallone in I play Rocky, portraying the actor's determination to become an actor and capturing his gravelly voice, muscular physique, while also recreating the iconic scene on Philadelphia's Rocky steps.