(CNN) Stephan Bonnar, the Ultimate Fighting Championship Hall of Famer who popularized the sport in the finale fight of the first season of "The Ultimate Fighter" reality show, died Thursday, the mixed martial arts promoter announced Saturday.
Bonnar died from "presumed heart complications while at work," the UFC said in a news release. He was 45.
"Stephan Bonnar was one of the most important fighters to ever compete in the Octagon," UFC President Dana White said in the release. "His fight with Forrest Griffin changed the sport forever, and he will never be forgotten. The fans loved him, related to him and he always gave them his best. He will be missed."
Bonnar's three-round light heavyweight final bout against Forrest Griffin in Las Vegas in 2005 saved the fledgling UFC, paving the way to the sport's popularity today. The fight is in the company's Hall of Fame fight wing, which recognizes "the greatest, most memorable and historically important UFC bouts."
Griffin won the epic match and was awarded a UFC contract. But the promotion also gave Bonnar a contract, too.
"I knew it was a good fight during the fight," Bonnar later said, according to the release. "It hit me when everyone started stomping their feet and it felt like the whole place was shaking. And that was in the second round. I was like 'oooh, this must be good.'"
"Everything changed. I didn't think I'd have a UFC career," he went on. "It was just a little hobby I was doing, so it changed everything. Almost overnight, I became like a celebrity. Everywhere I went, someone would recognize me, even in obscure places."
Known as "The American Psycho," Bonnar fought Hall of Famers such as Jon Jones, Rashad Evans, Anderson Silva, and Tito Ortiz during his seven-year light heavyweight career.
The Hammond, Indiana, native finished with a 17-9 UFC record, defeating fighters such as Krzysztof Soszynski, Igor Pokrajac, and James Irvin.