Maybe this story sounds familiar: It’s 1975, and a small-time fighter from a working-class, Northeast neighborhood gets an improbable chance to go toe-to-toe against a smooth-talking, hard-hitting champion. He has no shot to win—at least so everyone thinks, before he makes it 15 rounds with the champ.

It’s the fictional story of Rocky Balboa. It’s also the true story of Chuck Wepner.

Back in 1974, Wepner was the pride of working-class Bayonne, NJ—a family man and full-time liquor salesman who moonlighted as a small-time heavyweight boxer on the Jersey prizefighting circuit. That changed when boxing promoter Don King chose Wepner to fight Muhammad Ali, who had just ascended to the heavyweight throne after his own improbable victory against George Foreman. In that fateful fight on March 24, 1975, Wepner made it to the 15th round against Ali, even registering a knockdown before finally losing to the champion by technical knockout.

Wepner was an instant local hero. That fame went nationwide when a young actor named Sylvester Stallone launched Balboa’s story—which was allegedly inspired by Wepner—into the national canon.

On Friday, Wepner’s own story finds its way to the big screen in Chuck, a story of the “real-life Rocky.” And as Chuck makes clear, the Ali fight and Wepner’s own brush with movie stardom were only the beginning of a path into the dark side of fame and his ultimate redemption.

Chuck’s path to the movies was almost as long and winding as Wepner’s. Throughout the movie’s 10 years in development, multiple actors had been approached for the starring role, Wepner says, but none seemed right—until producer Mike Tollin mentioned a certain action star.

“When they told me that Liev Schreiber was gonna be playing me in the part, I jumped to it,” Wepner tells Men's Fitness. “Through the years, I've always thought he was the perfect actor [for the part].”

Initially, the boxing fan in Schreiber was drawn to Wepner’s tale. “I wasn’t familiar with Chuck Wepner’s story, and I felt like that was a grave error that we could try to correct,” Schreiber, who’s earned awards nods for his punchy performances in Showtime’s Ray Donovan, tells Men's Fitness.

But for Schreiber, now a father with a steady TV gig, Wepner’s time outside the ring—his fall, his incarceration, and ultimately his reconciliation—was the more gripping story. “As I thought about it, the cautionary tale about fame and celebrity that seemed to be at the heart of Chuck’s story got more and more compelling to me,” he says. “Fame is a Midtown bus going 50 miles an hour.”

The rest of the cast is stacked with talent. Wepner says Elisabeth Moss “is spectacular” in her role as his wife, Phyllis. (“She might even get a nomination,” he says.) Ron Perlman is Al Braverman, Wepner’s grouchy corner man. Jim Gaffigan plays perfectly to type as Wepner’s goofy pal John, both an emotional crutch and an anchor as Wepner sinks deeper into self-destruction. Michael Rapaport plays a fierce foil to Wepner’s earnestness as Chuck’s brother Don. Pooch Hall, who spars alongside Schreiber in Ray Donovan, plays Muhammad Ali.

The movie’s emotional fulcrum is Naomi Watts, who plays Wepner’s eventual (and current) wife Linda. In spending time with the Wepners, Schreiber noticed that Chuck habitually scanned the room to gauge people’s reactions to him, especially Linda. “That was really interesting to me, because he clearly needed and valued her in a way that I was touched by,” Schreiber says. “Knowing his story, I thought was pretty compelling. And honestly, I really, really wish we had more of Linda in the movie.”

“Liev and I have become real good friends over the last six months,” Wepner says. “I loved being with him, he's a great guy.”

Of course, Chuck is still a boxing movie. And while it’s not a documentary—although the movie eventually spun off an ESPN: 30 for 30 doc called The Real Rocky—Schreiber says he and director Philippe Falardeau wanted to match the Wepner-Ali fight “punch for punch.”

“Guys like Chuck are one in a million,” Schreiber says.

“One of the things I like about boxing is that a lot of times, it’s really messy—and then, all of a sudden, boom,” he says. “Even in that [Wladimir] Klitschko–[Anthony] Joshua fight, there’s a lot of nothing, a lot of nothing, and then whoa in the fifth round, whoa in the sixth round, boom in the 11th round. That’s three events in a 15-round fight.”

So whereas modern boxing flicks like Creed and Southpaw are full of flashy cuts and dramatic camera work, Chuck can seem a bit, well, ordinary. Falardeau revels in Wepner’s comparatively clumsy “Jersey-style” fighting, especially in Wepner’s pivotal battle against Ali. (Even Ali was “tired and overweight” during that fight, Falardeau noted.)

That’s on purpose, says Wepner: “In the movie, I say, ‘I'm gonna fight [Ali] Bayonne style—Jersey style: rough and dirty.’ That's the kind of guy I was. I was never graceful. I was just a big guy who's in great shape, a tough guy who can take a punch and could punch a little bit, and I was rough.” (Wepner, 78, now says he’s only 9 lbs heavier than his fighting weight of 228.)

But if there were one aspect that Schreiber sought to capture, it was his charismatic earnestness, which buoys the movie’s tenor even as Wepner’s life and family fall apart.

“Guys like Chuck are one in a million,” Schreiber says. “If you meet Chuck, you get a sense that there’s a real authentic toughness—not the mean or dangerous kind, but real toughness. More than that, he’s a terrific raconteur and great storyteller, and someone who is really eager to make a connection. Which is a really lovely quality about the character that I felt was really important to try to get.”

It’s a quality Rocky fans will immediately recognize. “That fight with Ali, anyone else looks at that, you think, ‘Jesus, 15 rounds of getting pounded by the greatest fighter that ever lived? What are you even doing there?’

“But that’s not Chuck. Chuck is like, ‘I’m going to whoop his ass.’”

Chuck, directed by Falardeau and starring Schreiber, Moss, Perlman, Watts, Gaffigan, Rapaport, and Hall, is in theaters Friday, May 5.