The movie created the "Vote for Pedro" T-shirt and made Napoleon's disgusted version of "gosh!" into a 2004 catchphrase.

Made for just $US400,000 by a group of recently graduated Brigham Young University film students, it would ultimately gross more than $US46 million after its June 2004 release. A word-of-mouth hit before Twitter and Facebook took off, it was part of a handful of independent comedies that took off in the early 2000s.

Napoleon Dynamite tells the story of its curly-headed, socially awkward title character who ultimately triumphs over the high school jocks and cheerleaders because of his quirks, rather than in spite of them.

Its success added to a rising profile for the world's unapologetic nerds at the beginning of a new wave of geek glory. The Big Bang Theory, would debut a few years later and become television's top-rated sitcom, while comic book movies achieved box office dominance.

The husband and wife team of Jared and Jerusha Hess mined true-to-life oddball high school moments, from a musical sign language club to puffy-sleeved dresses for school dances. There were also nods to rural life in the tiny city of Preston, Idaho, like the much-quoted line drawn from Napoleon's mealtime call to the family llama: "Tina, you fat lard, come get some dinner."

The combination struck comedic gold.

"I think the legacy of the movie is how original it is," said Glenn Williamson, an independent film producer and lecturer at the University of California, Los Angeles School of Theatre, Film and Television. "I like to think something else like that would find an audience today, because I do think people respond to that authentic freshness."

Shot in just over three weeks, the movie made a splash at the Sundance Film Festival even though it was submitted before director Jared Hess thought it was ready. But producer Jeremy Coon said he knew they had something special from the first edit.

"All of us were starving students coming out of school. A lot was riding on it," said Coon, who borrowed the money to make the movie from his brother.

Fox Searchlight snapped it up for nearly $US5 million, a princely sum at the time. It started off relatively small in theatres, but with clever marketing and word of mouth, people kept coming back. Nearly three months after its release, it was still earning just as much money per theatre, said Bruce Nash, founder and publisher of The Numbers, a movie industry tracking website.

It has a DIY aesthetic that reflects the way the movie was made: Napoleon's signature puffy snow boots were two decades old and borrowed from an uncle. Almost all the costumes came from thrift stores. His effervescent dance that wins the day at the movie's climax was mostly unchoreographed.

Jon Heder, who played Napoleon, went on to star with Will Ferrell in the comedy Blades of Glory in 2007 and in recent years has been doing TV and film voice work. The movie has also spawned a cartoon and, more recently, a comic book sequel.

A "Vote for Pedro" shirt showed up on San Antonio Spurs head coach Gregg Popovich in 2016, and actors from the teen drama Riverdale donned Halloween costumes based on the movie last year.

Original fans of the picture are now old enough to have their own kids, and it's a movie most parents wouldn't blush at showing their kids, Coon said.