Fearful that McDonald's might sue, an army of lawyers carefully vetted The Founder, a new film which tells the somewhat unflattering origin story behind the fast-food behemoth.

In the movie, which opens in Singapore tomorrow, Michael Keaton plays the controversial Ray Kroc, who in the 1950s began franchising the innovative California burger stand started by brothers Dick and Mac McDonald.

In 1961, he bought them out after a disagreement over how fast the chain was expanding. The film then shows him taking the credit for founding McDonald's and reneging on a handshake deal to pay the brothers 0.5 per cent of all future franchise revenue, which would have been worth billions.

Speaking to The Straits Times and other press in Los Angeles, the director, producers and cast admit that they, like many people, did not realise Kroc was not the real founder of McDonald's.

Aaron Ryder, 46, co-produced The Founder with actor Jeremy Renner and Renner's producing partner Don Handfield. He says when the idea for the film was mooted, "we had this meeting thinking, 'Why is the founder of McDonald's named Kroc?' And that's a question the movie answers".

But when Handfield, 45, tried to get the movie rights to a book that had been written about Kroc, who died in 1984, and McDonald's, he hit a roadblock. "The publisher said, 'Call McDonald's', and McDonald's had purchased the rights to these books and, I think, buried the authors in cement," he quips.

Things turned around when he tracked down Mr Jason French, grandson of the late Dick McDonald, who is played by Nick Offerman in the film.

Mr French wanted people to know Kroc was not the real founder of McDonald's and told the producer: "We've been waiting 50 years for someone to tell our story and you're the first one who's found us."

Handfield recalls: "He was really excited and gracious and that unlocked a treasure trove of information that they had - archival letters, dictaphone recordings of Kroc talking to the McDonald brothers - and it just launched from there."

Director John Lee Hancock (The Blind Side, 2009) says the McDonald's corporation did not try to stop the movie or influence it, but the film's lawyers made sure the production did not get factual details wrong so they would not end up in court.

"The first thing I asked when I interviewed for the job was, 'Can we do this?'

"And they said, 'Yes, under the doctrine of fair use, there's a historical element to this movie, so you can do it as long as it's exact,'" he says, referring to the legal principle allowing the fair and reasonable use of trademarks such as McDonald's without the copyright owner's permission.

"A journalist sent McDonald's a script a few weeks before we were going to start shooting, hoping to cause a dust-up and start a fight. And somebody from the McDonald's corporation read it and its official response was something like, 'Ray Kroc was a fascinating and talented man and it doesn't surprise us in the least that someone would make a movie about his life.'"

One of the tweaks the film's lawyers pushed for: a clarification that McDonald's no longer makes its milkshakes from a powdered mix, as the movie shows it doing for a period of time as a means to cut costs.

Hancock, 60, insists the film does not set out to demonise Kroc, who is given credit for his persistence and innovation in making McDonald's what it is today.

"There were two versions of this movie that would be very easy to make. One would be a Horatio Alger story of the little guy who has a big dream and now feeds 1 per cent of the world," he says, referring to the 19th-century American writer known for rags-to-riches tales.

"The other would be the evil monster Kroc, who is affecting the world in a negative way because of (McDonald's impact on) crops, et cetera.

"Both of those are not that interesting to me, and would be better documentaries, anyway. I'm more interested in something like the balance I felt there was throughout the script. I was actively pulling for Kroc in the first half of the movie, then going from feelings of ambivalence to head-scratching to, 'No. Gasp.'"

He and the producers agreed the best actor to bring Kroc to life was Keaton, the 65-year-old Oscar- winning star of Birdman (2014) and Beetlejuice (1988).

Keaton says the story is an important one to tell because of how McDonald's went on to transform the world's consumption habits. "It changed culture beyond food - we became a portable, disposable society and that's not overblowing this."

He points out that McDonald's continues to have a huge impact on the environment because of how much beef it uses, among other things. "I live on a ranch in Montana and lease my place to a guy who runs his cattle on it. We rotate how we graze because people don't realise what the impact is if you overgraze, environmentally and exponentially. It affects everything."

At the same time, he says Kroc's work ethic and sheer doggedness were unimpeachable - the man went from a struggling milkshake- mixer salesman in the 1950s to the world's first fast-food tycoon.

"When he was a teenager, he dropped out of school because he wanted to go to work. He was a driven guy and he wanted to get into business. And I think it was sheer will, determination and hard work.

"I found him not manipulative at all until maybe when he realises that he's in the real-estate business - everything turns right there," he says, referring to the moment in the story when Kroc sees the key to success for McDonald's is buying the land its restaurants stand on and renting it out to franchise operators.

"At that point, he started manipulating the brothers because he was in a power position," says Keaton, who was married to the late actress Caroline McWilliams and has a 33-year-old son.

The film also captures a moment that was a fork in the road for American capitalism, Handfield says.

"The McDonald brothers represent what I call sustainable capitalism, which is, like, have a great product and take care of your employees, and Ray Kroc represents the other side of capitalism, which is cut down every tree in the forest, make as much as you can, expand as far as possible.

"The brothers, I felt, were driven by love for their product and employees and Kroc was driven by fear - of not being a success, of being poor.

"These two things were battling for the soul of American capitalism and, ultimately, Kroc's version won."

•The Founder opens in Singapore tomorrow.