This story first appeared in the July 3 issue of The Hollywood Reporter magazine. 

In 2005, the Ultimate Fighting Championship — today, the world’s largest mixed martial arts promoter, with annual revenue of over half a billion dollars and more than 190 million fans worldwide — was deep in the red.

The ultra violent reputation of “human cockfighting,” as Sen. John McCain famously decried it after the sport launched in 1993, was holding it back from mainstream acceptance. Brothers and casino magnates Frank and Lorenzo Fertitta, who bought the company from its founders (entrepreneurs Art Davie and Bob Meyrowitz, jujitsu legend Rorion Gracie and producer Campbell McLaren) for $2 million in 2001, were looking at nearly $40 million in losses and needed more exposure than pay-per-view bouts could offer.

Fearing the sport would someday languish in the record books as a fringe curiosity, the brothers turned to prolific unscripted producer Pilgrim Studios, with whom they had partnered on the 2004 Discovery Channel docuseries American Casino, to pitch an MMA reality competition format called The Ultimate Fighter (TUF).

“All the networks were afraid of it,” says UFC president Dana White. Even Spike, the Viacom-owned cabler then only two years into its rebranding as “the first network for men,” shied away. So the Fertittas made a Hail Mary play, shouldering the $10 million production costs themselves and essentially making a time-buy on Spike for 13 episodes, including a live finale. White makes it clear that the stakes were high: “If the first season of The Ultimate Fighter didn’t work, the UFC would have folded.”

The Ultimate Fighter debuted in January 2005 with 16 aspiring fighters moving in together to train on rival teams coached by UFC pros Chuck Liddell and Randy Couture. Despite scant network or advertiser support — the matchups that concluded each episode took place in a blue octagon devoid of sponsor logos — TUF grew from an average 1.8 rating in the key 18-to-34-year-old male demographic (1.5 overall) for the first three episodes to 2.5 (1.8 overall) for the final three taped episodes. (Spike’s recent Lip Sync Battle premiere delivered a 1.8 rating among men 18-to-34.)

But entering the live finale in Las Vegas, The Ultimate Fighter‘s future remained uncertain. That’s when light-heavyweight finalists Forrest Griffin and Stephan Bonnar proceeded to go a punishing three rounds that seemed to showcase the full breadth of MMA techniques, from punches to wheel kicks to Muay Thai clinches. As the roar from the Cox Pavilion crowd (which included Hollywood fans Adrian Grenier and Kevin James) grew, more and more people at home were tuning in, too.

“People were calling their friends, saying, ‘Are you f—in’ watching this f—in’ network? You seeing the fight?’ ” says Pilgrim president and CEO Craig Piligian (in his signature colorful vernacular). After 15 minutes, Griffin prevailed by unanimous decision, but the real winner was the UFC itself.

While the UFC’s pay-per-view events rarely rose above 70,000 buys at the time, millions of cable subscribers were now exposed to The Ultimate Fighter. The show would run another 14 seasons on Spike until the UFC struck a seven-year, multimedia-rights deal with Fox in 2011 after a bidding war that reportedly reached an average of $100 million a year — a far cry from just six years prior, when the UFC had to pay to get on TV. And amid the organization’s proliferating content, The Ultimate Fighter was a key part of the agreement. “The show was essential to the ecosystem of the UFC in terms of allowing fans to connect with new fighters in ways that you can’t necessarily do just watching them in the octagon,” says Fox Sports head of business operations David Nathanson.

The Ultimate Fighter aired three seasons on FX before moving in 2013 to help launch Fox Sports 1, where it is the network’s most-watched series; new episodes air Wednesdays at 7 p.m. PT. Appetite for the show is so big that it’s spawned its own aftershow, TUF Talk, a dedicated half-hour immediately following each episode of the current season 21, which pits two rival South Florida gyms against each other with $500,000 on the line. It’s not the first time the show has experimented with its format: Season 15 was completely live but was declared a bust — “you didn’t really get to know who the fighters were, so you weren’t invested,” says Piligian — while season 18 tapped Ronda Rousey and Miesha Tate to coach two coed teams.

“Adding women was a no-brainer, particularly since arguably the most decorated and popular fighter in the UFC is Rousey,” says Nathanson. The show doubled down a year later with an all-female contestant pool for season 20, whose premiere in September attracted 2.54 million viewers — a high for the show since moving to Fox — and whose finale doubled for the first time as a UFC title bout, for the newly created women’s strawweight class.

That championship fight was just one of the ways The Ultimate Fighter has made a unique impact on the unscripted format — and in turn boosted the sport that spawned it. “It’s become like a farm league for the UFC,” says Ralph Wikke, a producer on the show since the beginning. “You invest in contestants on other reality shows, then at the end of the season they go away and you never see or hear from them again,” White says. “If you win The Ultimate Fighter, you come right into the UFC and start fighting all the people you idolized for years. You can continue to follow these people for their whole careers.”

Adds Piligian: “What this reality show was able to do was take a fringe sport and make it a global brand.” He’s not exaggerating — in addition to the U.S.-based Ultimate Fighter, which airs around the world, the franchise has spawned multiple international editions, including versions in Brazil, Australia and China.

The UFC itself also has come a long way since a decade ago, when it was in danger of being lumped alongside other failed “extreme sports” ventures like the XFL. Instead, its president is making cameos on Silicon Valley and The Mindy Project, while Rousey has become a bona fide celebrity, logging numerous high-profile acting roles in such films as Expendables 3, Entourageand Furious 7. UFC’s expanding empire now includes more than 100 licensed gyms across the country, a video game franchise and, of course, the reality show that helped save the whole enterprise.

“Once the world saw that these guys weren’t animals or barbarians, we got to show everybody who they really were and how beautiful and technical the sport really is,” White says.

Piligian too is proud of the show’s impact and says its appeal extends far beyond TV’s typical reality-competition offerings. “On other shows, contestants gotta sing against each other, cook against each other, sew against each other,” he says. “On our show, these guys live together, they sit down and eat Pop-Tarts together, and then at some point they are locked in a cage and they gotta beat the ever-living f— out of each other.”