Ultimate Fighting Championship Hall of Famer Stephan Bonnar, who popularized the sport in the finale fight of the first season of “The Ultimate Fighter” reality show, died on Thursday at the age of 45. The UFC said in a news release that Bonnar died from “presumed heart complications” while at work.

UFC President Dana White said in the news release: “Stephan Bonnar was one of the most important fighters to ever compete in the Octagon. 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 match against Forrest Griffin in Las Vegas in 2005 paved the way to the beginning of the popularity of the UFC. 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 match and was awarded a UFC contract, but also gave Bonnar a contract. Bonnar later said: “I knew it was a good fight during the fight. 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. 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.”” Bonnnar, known as “The American Psycho,” went on to fight against Hall of Famers such as Jon Jones, Rashad Evans, Anderson Silva, and Tito Ortiz during his seven-year light heavyweight career.

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