Stephan Bonnar, UFC Hall of Famer, died on Thursday at the age of 45.

"Stephan Bonnar was one of the most important fighters to ever compete in the Octagon," UFC President Dana White said in a statement. "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."

CLICK HERE FOR MORE SPORTS COVERAGE ON FOXNEWS.COM

Bonnar is considered a pioneer for the UFC, as he made a name for himself on the first season of "The Ultimate Fighter." He finished as that season's runner-up to Forrest Griffin in a fight that is widely known as one of the greatest fights of all time. White has called the fight one of the driving forces behind the success of UFC, and the fight almost singlehandedly put the two fighters in the Hall of Fame in 2013.

"I knew it was a good fight during the fight," Bonnar once said of the epic three-rounder. "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," Bonnar also said. "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. I was traveling with Tapout and we were in a small town. I was jogging and someone in a pickup was going ‘Hey Bonnar.’ And everywhere you go, someone knows who you are. It was wild." 

UFC'S JOE ROGAN URGES THE ROCK TO 'COME CLEAN' ABOUT PHYSIQUE

Bonnar fought to a 17-9 record and had battles with UFC legends Jon "Bones" Jones, Anderson Silva, and Tito Ortiz – the latter two fighters were his final opponents.

His victory over Krzysztof Soszynski at UFC 116 was named the Fight of the Night, despite the headlining match being between Brock Lesnar and Shane Garwin.

UFC said he died of "presumed heart complications."