How Zac Efron Bonded with 81-Year-Old Hero Who Inspired His Wild New War Movie: 'I Was Honored'

When Zac Efron signed on to star in the new movie The Greatest Beer Run Ever, he happily embraced the typical performance challenges of portraying a real person and filming in extreme weather for the film's fictional war zone scenes. What he didn't expect was to forge a lasting connection to the man who inspired it all.

"The stakes feel a lot higher," Efron, 34, tells PEOPLE of playing real-life living hero John "Chickie" Donohue. "I wanted the end result to be a movie that he'd be proud of and a performance that he'd be proud of. So living up to that definitely made me work extra hard."

The film is inspired by Donohue's incredible and improbable five-month goodwill mission in 1967 when the then 26-year-old New York native and merchant mariner boarded a cargo ship and traveled to the front lines of the Vietnam War to bring beers to his friends serving there.

Courtesy of Apple

"It's one of those unbelievable real-life scenarios that you just can't believe a guy got himself into," says Efron. "It's a beautiful story about human nature, love and a really difficult war and time in history."

The Greatest Showman star and Donohue, now 81, met during filming in New York and instantly connected, despite one not being particularly familiar with the other.

RELATED: Watch Zac Efron Accidentally Go to War in an Exclusive First Look at 'The Greatest Beer Run Ever'

"When we were filming the New York scenes, Chickie was pretty much on-set every day," says Efron. "My first impression, I was just honored, you know? I was happy he was there and that he seemed to be liking what was going on. He was always available for questions. I could ask him virtually anything, and he would always have a good answer."

Apple TV+

Adds Donohue: "I've never been involved in this type of thing before, so I did not know what to think," he says. "I didn't know him. [To Efron] All my kids know about you, but I didn't know about you, so there was no impression that I could grab hold of. But he treated me like an equal. And being in someone else's world and being treated by a professional in that world, I took it as a compliment. So instinctively I said, 'I like this guy!'"

Most people who encounter the real-life story, first detailed in the New York Times bestseller and the 2020 bestseller The Greatest Beer Run Ever: A Memoir of Friendship, Loyalty, and War by Donohue and J.T. Molloy, can't believe he actually succeeded in finding his friends in Vietnam, let alone bringing them beers.

"One of the most impressive things about Chickie and this whole adventure is that there were so many opportunities when he could have turned back or quit," says Efron. "Everybody's advice was 'Stop! You don't need to do this.' And none of that fazed him. He was doing what he genuinely thought was right. And knowing some of the risks he faced heading into the [combat zones], I was very nervous when I was just playing it; I can't imagine the reality."

Donohue went on to work in construction and a union official but is now retired in Florida living with his wife of 52 years, Theresa, and is the proud grandpa of seven. He maintains that he was simply doing the right thing.

For much more on Zac Efron and Chickie Donohue, pick up the latest issue of PEOPLE on newsstands Friday

Apple TV+

RELATED: Zac Efron Gets Candid About His Agoraphobia: 'I Just Don't Go Out'

"I had no mission to teach anybody anything," he says. "My mission was simply to let the guys over there know that we truly, truly supported them. Just like our fathers who saw action in World War II, they did their duty for their country, and it had nothing to do with politics. People often ask me: 'Why did you do it?' I'd say to myself, 'Why can't they just accept that it was the right thing to do?' That's all it really was. I didn't know what was going to happen exactly."

He also fully supports the big screen adaptation and Efron's portrayal in particular.

"Everybody has been so nice to me," says Donohue. "I'm not just blowing smoke here, but my friends ask me: "Did you see the movie?" I say "Yeah, I've seen it twice." And they say, "This guy who's playing you, what did you think?" I said, "It scared the crap out of me because the guy played me better than I play myself!" Forget about the appearance. It was the attitude and the feeling. I got emotional."

Adds Efron: "There's an incredible amount of innocence and bravery and honor in what he accomplished. I couldn't ask for a better character to play. It was an honor and a pleasure."

The Greatest Beer Run Ever is playing in theaters and streaming on Apple TV+ Sept. 3