It’s not that Sundance festival director John Cooper wasn’t always a “movie guy.” It’s just that, prior to joining the staff 25 years ago, he had dedicated most of his creative energy to the stage.

Turns out Cooper’s collaborative New York theater experience was a fitting background from which to dive into the idealistic indie-film org. Back then, Sundance was still finding its identity. It wasn’t even Sundance yet, but rather the Utah/U.S. Film Festival, a pokey regional sprocket opera conceived by Robert Redford as a platform to support films made in “the hinterlands” over Hollywood.

“I didn’t know any filmmakers when I lived in New York. But I was looking for a way to move to Los Angeles,” admits Cooper, who viewed his first brush with Sundance — handling administrative duties for the 1989 Directors Lab — as a summer gig. But something about that dynamic hooked Cooper, who responded to the backstage intimacy and creative energy of helping aspiring filmmakers develop their projects. (Quentin Tarantino passed through the Lab in 1991 with the script that became “Reservoir Dogs.”)

As it happens, Cooper’s first year, 1989, was the moment everything changed for Sundance — and the indie film biz in general — as Steven Soderbergh’s “Sex, Lies and Videotape” launched a bidding war in Park City, got invited to Cannes (where it won the Palme d’Or) and proved that films made outside the system could generate serious revenue.

“There was starting to be this expression, mostly on 16mm, of filmmakers that were going to make a different kind of American film,” says Cooper. The team looked to a series of Johns as models: Cassavetes, Waters, Sayles and producers rep Pierson. The Coen brothers had made “Blood Simple” and Susan Seidelman directed “Desperately Seeking Susan” outside the system. “It wasn’t so much that we discovered (this movement) as there was a place for more. And it started to happen very quickly after that.”

In September, after the Directors Lab let out, Cooper continued to dabble in theater. (He helped mount the West Coast production of “Really Rosie,” meeting — and being mentored by — Maurice Sendak. “He taught me about perfection,” Cooper says.) But his mind was already in the movie world. The next year, he managed the Lab and also joined the festival programming team, then just three people, headed by Tony Safford.

“It all seemed renegade and maverick, like we were making it up as we went,” says Cooper, who saw an opportunity to spearhead the festival’s emerging shorts program, reaching out to film schools and growing the submissions pool from 100 or so to 1,500 — all of which he was responsible for watching himself.

Cooper quickly realized he had an eye for spotting talent, recognizing nobodies who went on to become some of the biggest names in indie film: David O. Russell, Paul Thomas Anderson and Alexander Payne. He remembers tipping off former L.A. Times critic Sheila Benson to his favorite shorts, which she would make a point of seeing at the fest. “I felt like a baseball scout,” he says.

As Sundance grew, so did Cooper’s role within the organization. In 2003, he stepped up to director of programming, becoming fest director in 2009. “Redford has always been clear on what Sundance is supposed to be,” he says. “I’ve had to help him see that it can be bigger.” Over time, what had started as a “scrappy” indie showcase became the main game in town.

Being selected by Sundance made many a film’s career. Rejection ruined others. Asking prices escalated. Movie stars slummed, taking scale to earn their serious-actor cred, while off-the-radar helmers landed agents and fat studio directing deals. In short, the entire American film business shifted in response to the phenomenon that Cooper had witnessed firsthand in Park City.

Today, it’s hard to imagine the indie world without Sundance, or a time when the event felt small time compared to such events as Toronto and Telluride, Filmex and the IFP Market.

“We were always ‘the other.’ When people act like we’re not, I think, ‘Really? Are we establishment?’ ” Cooper marvels. “That’s why we concentrate on keeping ourselves as vital as we can. We’re never going to be what Cannes is to the cinema world. We’re always going to be about fresh and new … the discovery of ‘the other.’ What we do takes a lot of energy.”