NEW YORK • Mr Warren Buffett is not exactly an unknown quantity.

As the United States' most famous investor and the possessor of what Forbes estimates is a US$74- billion (S$105.4-billion) fortune, he has been the subject of endless scrutiny across print and film, most without his participation.

But to him, one of the appeals of agreeing to let the cameras into his life for Becoming Warren Buffett, an HBO documentary that premiered in the US yesterday, was to tell his story in a relatively new way.

Nowhere are there in-depth discussions about balance sheets and cash flow, though there are flashy animations illustrating basic investing principles.

Instead, the film focuses on how Warren Edward Buffett grew from the Nebraskan son of a congressman to become the Oracle of Omaha, the avuncular mascot of American capitalism who built Berkshire Hathaway into a US$406-billion empire and shows some of his warts along the way.

"People watching it expecting to learn how to buy cheap stocks will be disappointed," Mr Buffett said with a chuckle during a telephone interview. "When I think about getting beyond a financial audience, this becomes really prominent."

The film, directed by film-maker Peter Kunhardt, is indisputably positive towards its subject, showcasing hallmarks of the Buffett legend such as his regular chats with students, his poring through thick corporate financial statements and his almost daily visits to a McDonald's drive- through.

But the film does not shy away from portraying Mr Buffett, now 86, as something of a remarkable human computer, gifted with numbers and less so with interpersonal relationships.

He is the kind of man who straightforwardly says that he cannot remember the colours of his bedroom walls, and the kind of husband who, when his wife had the flu and asked for a pot to keep by her bedside, instead fetched a colander.

In the film, his daughter, Susie, says she learnt how to talk in sound bites to a father more immersed in financial issues than his children's. "You lose him to some giant thought he had in his head at the time," she said.

Mr Buffett does not quibble with what is on-screen.

"It's really an accurate portrayal," he said. "I make no claim to perfection."

Ms Susie Buffett, in a telephone interview, said she hoped the film captured Warren Buffett in full.

"I think people get so star-struck with the money and the fame, and they don't know that he's just a person," she said.

Becoming Warren Buffett is not the first work to look at the man as well as the investor.

Mr Buffett cooperated in the writing of The Snowball, an authorised biography by Alice Schroeder that the mogul is less than fond of these days. (He says diplomatically that the book was good in many ways, but also had errors.)

But the effect is different when the film features dozens of old family photos and interviews with Mr Buffett, his sisters and his children, and Microsoft founder Bill Gates and his wife Melinda.

Mr Buffett's first wife and the mother of his children, Susan (who died in 2004), is featured so prominently as an influence and force in his life that she is virtually a co-star.

Getting Mr Buffett's cooperation took some work, said Kunhardt, who had made documentaries about writer Gloria Steinem and United States senator Ted Kennedy.

He said that he approached Mr Buffett's son Peter in the autumn of 2014 before writing "an old-fashioned letter" to Mr Buffett, which Peter placed on his father's desk.

"I'm a non-finance guy, so I wanted to do a film about Warren the man and how Warren the man became Warren the super-successful investor," Kunhardt said.

A week later, Mr Buffett - impressed by Kunhardt's previous work - agreed to the first of four sit-down interviews.

By 2015, Ms Buffett presented the film-maker with a treasure vault for Buffettphiles: closets and cardboard boxes full of family photos, personal documents and home movies never seen publicly.

Mr Buffett remained closely engaged with the project. This month, as the movie neared completion, he caught a numerical error in one of its graphics, a missing handful of zeros in one particular datum.

One notable omission in Becoming Warren Buffett is any interview with Astrid, Buffett's current wife.

When Susan left Mr Buffett in 1977 to move to San Francisco, the two remained married.

She later introduced him to Astrid, who became his longtime companion with her blessing.

After Susan (whom Mr Buffet also called Susie) died in 2004, he married Astrid.

"Susie and I and Astrid had an arrangement that worked maybe one time in a thousand," he said.

Nonetheless, he said that he asked Kunhardt to respect Astrid's wishes not to be interviewed.

For his part, the film-maker said he retained full editorial control and decided that Susan was simply a much more vital part of Mr Buffett's story.

And she is a huge part of Becoming Warren Buffett, from Mr Buffett's courtship of her to their raising their three children, thanks to a lengthy interview she gave talk-show host Charlie Rose in 2004.

She is credited with helping to shape Mr Buffett's liberal politics - along with a reaction to his beloved father's conservative principles - through her interest in the civil rights movement.

And Mr Buffett credits his first wife with being the proper parent for his children and for helping push him into philanthropy. He has pledged to give away 99 per cent of his fortune.

"The part that I liked best is that they get to see Susie," he said of his first wife and the movie's prospective audience.

"What happened with me would not have happened without her."

Though he is an octogenarian and has battled prostate cancer (successfully), he insists that participating in the movie was not a way to cement his legacy. "This was not done because I think I'm getting my last haircut next week," he said. "At 86, I know what's in the books, but literally I get to do what I love and it's easy for me," he added. "I do not feel that my life is past its most interesting points."

NYTIMES