Director Reed Cowan's documentary on the Mormon Church's decades-old involvement in the fight to ban gay marriage in the United States premiered Sunday to a thunderous standing ovation.

8: The Mormon Proposition had its world premiere at the Sundance Film Festival underway in Park City, Utah, just 30 miles from the world headquarters of the Church of Jesus Christ of Latter-day Saints.

In a series of interviews with Mormon Church leaders, gay activists and Utah politicians, Cowan shines a bright light on the church's profuse involvement in banning gay marriage throughout the nation since the early 1990s. The film's focus, however, is on California's 2008 fight over Proposition 8, the ballot measure that outlawed gay marriage in the state.

“So much of what we were fighting was perpetrated here [in Utah],” San Francisco Mayor Gavin Newsom told the Salt Lake Tribune after attending Sunday's premiere.

Californians Against Hate founder Fred Karger, who is interviewed in the film and attended the film's screening, said the film will “undoubtedly change history.”

“Incredible movie and experience,” Karger said referring to the large crowd and the film's standing ovation.

Cowan first interviewed Karger in San Francisco. The pair met in front of the Castro Theater on Wednesday, March 4, 2008 just as a huge gay marriage vigil was about to step off. Karger spoke to the filmmaker two more times over the course of the next year.

Mormon officials have refused to comment on the film, saying it is “obviously biased.”

“Judging from the trailer and background material online, it appears that accuracy and truth are rare commodities in this film,” spokeswoman Kim Farah told the AP. “Although we have given many interviews on this topic we had no desire to participate in something so obviously biased.”

In a blog post, Cowan said the film had divided his family.

“My determination [to finish the film] has been tested. At this writing, I have lost communication with my sisters and my mother and my father. They are wonderful people and they are Mormons. The fear they have over what this film will say has worn thin to the point that our relationships are stressed and I fear broken forever,” he said.

A planned protest of the film failed to materialize, but a small group of gay marriage activists chanted “Separate, church from 8” outside the premiere.