Diane Weyermann, who oversaw the making of potent documentaries like “An Inconvenient Truth,” “Citizenfour” and “Food Inc.,” and in so doing helped change the documentary world from an earnest and underfunded backwater of the movie industry into a vibrant must-see category, died on Oct. 14 at a hospice facility in Manhattan. She was 66.

Her sister Andrea Weyermann said the cause was lung cancer.

“Diane was one of the most remarkable human beings I have ever known,” Al Gore, the former vice president and presidential candidate whose seemingly quixotic mission to educate the world about climate change through a decades-long traveling slide show became an unlikely hit film with an odd title, “An Inconvenient Truth,” said in an interview. “She was enormously skilled at her craft and filled with empathy,” he added. “It is not an exaggeration to say she really did change the world.”

So did his movie. “An Inconvenient Truth” earned an Oscar in 2007, and Mr. Gore won the Nobel Peace Prize that same year, sharing it with the Intergovernmental Panel on Climate Change. The film, which became one of the highest-earning documentaries ever made, was the second documentary made by the activist film company Participant, where Ms. Weyermann was a longtime executive, and hardly anyone in Hollywood thought it was a good idea. It was a movie about a slide show, after all.

When the filmmakers screened it for a major studio in hopes of getting distribution, some of the executives fell asleep. “There was audible snoring,” recalled Davis Guggenheim, the director, “and when it was over one of them said, ‘No one is going to pay a babysitter so they can go to a theater and see this movie, but we’ll help you make 10,000 CDs for free that you can give to science teachers.’”

Dejected, Mr. Guggenheim, Mr. Gore, Ms. Weyermann and others repaired to a steakhouse in Burbank, Calif., to brood, but Ms. Weyermann refused to be cowed.

“Just wait till Sundance,” she said.

“An Inconvenient Truth” received four standing ovations at the Sundance Film Festival, and Paramount bought the distribution rights.

Participant had been started in 2004 by Jeff Skoll, a social entrepreneur and the first president of eBay, with its own mission: to make movies about urgent social issues. A former public interest lawyer, Ms. Weyermann was running the documentary program at the Sundance Institute when Mr. Skoll hired her in 2005, though he was worried that Robert Redford, a friend and the founder of the institute, would be irked. (He wasn’t, and blessed the move).

“From the start, Diane brought knowledge, relationships, context and industry insights into our team,” Mr. Skoll said in an email. “Participant was a small, burgeoning company at the time, direct film industry expertise was limited, and we had very little documentary experience.”

Participant would go on to make over 100 films, including the features “Spotlight,” “Contagion” and “Roma” and the documentaries “My Name Is Pauli Murray” and “The Great Invisible.”

“Diane built an incredible slate of films that have made a difference in everything from nuclear weapons to education to the environment and so much more,” Mr. Skoll added. “She was the heart and soul of Participant.”

It was Ms. Weyermann’s job to find, fund, form and promote documentaries from all over the world, and she traveled constantly doing so.

In 2013, Laura Poitras, the director of “Citizenfour” — the Oscar-winning tale of Edward Snowden, the National Security Agency contractor who exposed the government’s widespread surveillance programs — was holed up in Berlin when Ms. Weyermann came to see her.

“Diane knew I couldn’t travel to the U.S.,” Ms. Poitras said, because she was worried that she might be detained or arrested; during the course of her reporting, Mr. Snowden had become a fugitive and a cause célèbre. “She wanted to make sure I was OK, and I wanted her to see the cuts. I had hundreds of hours of film, and I told her right off, ‘I’m not going to be able provide any documentation’” — film studios typically require detailed written proposals — “and she immediately said, ‘We’re going to do this and I’ve got your back.’”

“She loved being in the editing room,” Ms. Poitras added. “She had an amazing ability to see a film when it was really raw and be in tune with it and what the filmmaker needed. You wanted her notes; she always made the work better.”

“A director’s whisperer” is how Mr. Guggenheim described her.

It wasn’t just the big box-office movies she supported, said Ally Derks, the founder of the International Documentary Film Festival Amsterdam. “It was the small, fragile films she nurtured too. She was in India with Rahul Jain, whose movie about pollution in New Delhi just screened at Cannes. She was in Siberia with Viktor Kossakovsky” — the Russian filmmaker whose 2018 film, “Aquarela,” has barely any dialogue or human beings and takes an immersive look at water, from a frozen Siberian lake to a waterfall in Venezuela to glaciers crumbling in Greenland.

Ms. Weyermann also championed Mr. Kossakovsky’s 2020 film, “Gunda,” about a winsome Norwegian pig, a movie similarly devoid of dialogue (or even people), music and voice-overs. In her review for The New York Times, Manohla Dargis called it “sublimely beautiful and profoundly moving” and noted that while funding movies is always difficult, “funding documentaries like this is heroic.”

Diane Hope Weyermann was born on Sept. 22, 1955, in St. Louis. Her father, Andrew, was a Lutheran minister; her mother, Wilma (Tietjen) Weyermann, was a homemaker and later worked for a glassware company.

Diane studied public affairs at the George Washington University in Washington, graduating in 1977, and four years later earned a law degree from the Saint Louis University School of Law. She worked as a legal aid lawyer before attending film school at Columbia College Chicago, graduating in 1992 with an M.F.A. in film and video.

That same year, “Moscow Women — Echoes of Yaroslavna,” her short documentary film about seven Russian women, filmed by a Russian and Estonian crew, was screened at Ms. Derks’s festival in Amsterdam. She also made a short film about her father’s hands.

Ms. Weyermann turned from making movies herself to helping others make them in 1996, when she became director of the Open Society Institute’s Arts and Culture Program, one of the billionaire investor George Soros’s philanthropies, now known as the Open Society Foundation. She started the Soros Documentary Fund, which supported international documentaries that focused on social justice issues. When she was hired by the Sundance Institute to set up its documentary film program in 2002, she brought the Soros Fund with her. There she set up annual labs for documentary makers, where they could work on their films with others, creating the sort of community that documentarians craved.

In addition to her sister Andrea, Ms. Weyermann is survived by a brother, James. Another sister, Debra Weyermann, an investigative journalist, died in 2013.

When Ms. Weyermann became co-chair, with the screenwriter and producer Larry Karaszewski, of the foreign-language film category for the Academy Awards in 2018, they promptly changed the name of the category to “international feature film,” pointing out that the word “foreign” was not exactly inclusive. “Diane had a way of cutting through everyday nonsense,” Mr. Karaszewski said.

In a 2008 interview, Ms. Weyermann was asked if she thought it was asking too much for a film to make a change in society.

“When films are made solely for that purpose they fall like a lead balloon,” she replied. “What I love about film is it’s a creative medium. It’s not just ‘Let’s focus on an issue and educate,’ but ‘Lets tell a story, let’s tell it beautifully, let’s tell it poetically. Let’s tell it in a way that isn’t so obvious.’”