There was a moment when it seemed everyone was about to release a movie about martial arts teacher Ip Man, his student Bruce Lee or Apple founder Steve Jobs.

That seems to have died down, but biographical pictures, or biopics in short, are going strong as a genre.

This week sees the release of The Founder, the story of Ray Kroc, who shaped McDonald's into a fast-food giant.

It seems obvious why studios churn out biopics - the public's appetite for celebrity information is insatiable, so there is a clear monetary reason to make a movie about Lee or Jobs. But why would a studio want to produce a portrait of Kroc, a businessman whose name has zero ticket-selling power?

The answer is this: More than any other kind of movie, films based on the lives of real people win awards.

On this year's list of Best Picture nominees at the Oscars, three of the nine pictures in the running are based on real events.

The three nominees (Lion, Hidden Figures and Hacksaw Ridge) are part of a trend years in the making. Biographical movies nabbed the Best Picture prize in 2015 (Spotlight), 2013 (12 Years A Slave), 2012 (Argo), 2010 (The King's Speech) and 2009 (The Hurt Locker).

Go further back and there are Gandhi (1982) and Amadeus (1984).

These movies win not because Academy voters adore non-fiction. They win because voters value artistic merit, dismissing works they consider cheap or exploitative. This bias eliminates horror, comedy and action movies, leaving only dramas and the rare fantasy and science- fiction work.

As a by-product of such filtering, biopics, which tend to be sober and dramatic, become over-represented on the nomination lists.

And if the story is about a person involved in a civil or social rights battle, the chances of it getting shortlisted shoots up because voters also love movies that can make a change in the real world.

One example is the feature based on the lives of black women who worked at the National Aeronautics and Space Administration in the United States. Hidden Figures is up for three Oscars (Best Adapted Screenplay, Best Picture and Best Supporting Actress for Octavia Spencer). It opens here on Feb 23.

Last year's Best Picture winner Spotlight described the work of reporters writing about child sex abuse by Catholic priests.

Nominees in the same category in 2015 included The Imitation Game, The Theory Of Everything and Selma. The first two depicted researchers fighting though their mental and physical shortcomings, while the third was based on a famous protest march led by Martin Luther King Jr and other leaders.

In a self-reinforcing cycle, "prestige" biopics - the sort that win awards, not the ones that cash in on celebrity - attract brand-name actors looking for a meaty role and another feather in the cap.

The Founder features Michael Keaton in the role of the ruthless tycoon who built a corporation spanning the globe. After Tom Hanks turned down the part of Kroc, producers went on a search.

In an interview with USA Today, director John Lee Hancock said he courted Keaton mostly because of the actor's attention-getting Oscar- nominated performance in Birdman (2014). "Birdman made it an easy choice," he said.

Keaton jumped in immediately.

Other actors eager to be in prestige biopics include Jonah Hill, who not only begged to be in the Jordan Belfort biopic The Wolf Of Wall Street (2013), but also agreed to a minimum-wage fee of US$60,000, rather than his usual millions.

George Clooney took home a measly US$120,000 for directing and co-writing Good Night, And Good Luck (2005), a portrait of journalist Edward R. Murrow. It would go on to get six Oscar nominations, including Best Picture and Best Directing for Clooney.

Biopics, however, come with their own set of legal problems in the areas of defamation and copyright.

Some are based on sources authorised by the subject. Lion, the story of Indian orphan Saroo Brierley, is based on his autobiography. Hacksaw Ridge, about non-violent war hero Desmond Doss, relies on a documentary about him.

But The Founder, which portrays Kroc as a ruthless man, is based on unauthorised writings. So is Jackie, about Jacqueline Kennedy, wife of former US president John Kennedy. It opens next week.

While no member of the Kennedy family seemed to have objected to the film Jackie, and the same goes for The Founder, their scripts were almost certainly thoroughly checked for anything that might trigger legal action because studios want films to generate money, not lawsuits.

But stories need villains and the simplest solution is a name change. This strategy does not always work.

A former employee of the "pump and dump" brokerage at the centre of The Wolf Of Wall Street had sued the film's makers, despite his name not appearing anywhere in the picture. His lawyers claim there are enough indirect details to identify him.

Mr Jerry Heller, former manager of rap group N.W.A., slapped a US$110-million (S$155.5-million) suit on the producers of Straight Outta Compton (2015) for what he considered a defamatory portrayal.

In the film, Paul Giamatti played Heller.

Other high-profile court actions include the one launched by the widow of fishing boat captain Billy Tyne, who died in the hurricane depicted in A Perfect Storm (2000). The film implied that he was incompetent, the widow alleged. She lost, but the court battle lasted years.

These days, social media gives disgruntled relatives an effective platform to take down a film they hate.

Lee's daughter Shannon made a Facebook post calling unauthorised biopic Birth Of The Dragon (2016) a "travesty on many levels". Fans shared the post nearly 2,000 times, which generated 580 comments, nearly all supporting her message.

Shannon Lee would envy the power musicians have over their life stories. If musicians or their families want to cripple a biopic, they only have to say "no" to song rights requests. Imagine the Johnny Cash biopic Walk The Line (2005) without his iconic tunes Folsom Prison Blues or Ring Of Fire or the Ray Charles story Ray (2004) without I Got A Woman or Georgia On My Mind.

Some film-makers are brave enough to do it anyway. The John Lennon biopic Nowhere Boy (2009) got around the rights problem by using rock hits from other artists. The Jimi Hendrix film, Jimi: All Is By My Side (2013), used the same trick, but the lack of Hendrix songs in a movie about Hendrix did not go unnoticed and it tanked.

The next time you look at the label "based on a true story", think about what it took to bring it to the screen - the awards strategy, the legal fees, the rights clearances - and it might make you see the movie in a new light.

•The Founder opens tomorrow and is reviewed on The many faces of pain.