FILE - In this March 26, 2013 file photo, attorneys David Boies, left, and Theodore Olson, addresse members of the media outside the Supreme Court in Washington. Olson and Boies fought on opposite sides of the case that determined the 2000 presidential election, but the veteran attorneys joined forces to defeat California’s gay-marriage ban, a five-year effort documented in “The Case Against 8,” which premiered at the Sundance Film Festival. The film follows the attorneys and plaintiffs in the lawsuit that resulted in the marriage ban being overturned. “The Case Against 8” is set to air on HBO in June. (AP Photo/Pablo Martinez Monsivais, File)

PARK CITY, Utah - Attorneys Ted Olson and David Boies once argued the Bush v. Gore case in front of the U.S. Supreme Court, but they say fighting California's law prohibiting same-sex marriage is the most significant thing they've done.

The two courtroom veterans fought on opposite sides of the case that determined the 2000 presidential election, yet they joined forces to defeat California's 2008 gay-marriage ban, Proposition 8. Their five-year effort is documented in "The Case Against 8," which premiered at the Sundance Film Festival in Park City, Utah.

The film follows the attorneys and plaintiffs in the lawsuit that resulted in the marriage ban being overturned last year.

"This is the most important thing I've ever done, as an attorney or a person," Olson says in the film, which won a directing award at the festival Saturday for filmmakers Ben Cotner and Ryan White.

Cotner, 34, and White, 32, gained access to the attorneys and plaintiffs in the case when the American Foundation for Equal Rights first filed its lawsuit in 2009. The film chronicles the case as the legal team and the two gay couples named as plaintiffs in the suit take it through California state courts and then to the U.S. Supreme Court.

"That's the luckiest job you could have as a filmmaker and a gay person," White said.

Olson and Boies said seeing their landmark case in the form of a film "was a really wonderful experience."

"Most of our cases involve a plaintiff and a defendant and a winner and that's it — although Bush vs. Gore was a little different," Olson said. "This involves tens of thousands of people in California, but really millions of people throughout the United States and beyond that to the world."

He and Boies have been deeply moved by their involvement with the case and the "seismic shift" in legislation and public opinion that followed. When they began arguing against proposition 8, only three states permitted same-sex marriage. Now it's 17, Olson said.

"There's been a remarkable transformation, and for us to have been a part of that is really extraordinary," he said.

"For all of us," Boies added, "it's probably the most important case, both in terms of the impact on the law and the impact on people."

"It really doesn't, as a lawyer, get more fulfilling," said Ted Boutrous, who also served on the legal team challenging the constitutionality of Proposition 8. "(It) just doesn't happen in that many cases where people around the country thank you and hug you."

The film is set to air on HBO in June, but the filmmakers plan to spend the next six months hosting grass-roots screenings and bringing the film to festivals around the country. They hope Olson — who represented the Republicans in the 2000 case — will draw more conservative viewers to take a look.

"One of the things he says in the film is marriage is a conservative value," Cotner said. "The fact that he's such a prominent conservative figure will hopefully pique people's curiosity about the film that otherwise might not be interested in a gay marriage film."

Said Olson: "Everybody who sees this film is going to be affected by it."

Meanwhile, the attorneys enjoyed feeling like celebrities during their week at the Sundance festival.

"Everybody's been very nice to us," said Boutrous, "even though we're lawyers."

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News from © The Associated Press, 2014