Fighters react to Stephan Bonnar’s sudden death at 45: 'Changed the landscape of the sport'

Several professional fighters took to social media to respond to the sudden death of UFC Hall of Famer Stephan Bonnar, who passed away Thursday. He was 45.

The UFC announced Saturday that Bonnar died of "presumed heart complications" on Dec. 22, prompting several people including UFC President Dana White and others to remember his legacy and impact on the sport.

In a statement, White highlighted the role of Bonnar, who donned the nickname "The American Psycho," in getting "The Ultimate Fighter" series off the ground.

Bonnar, a finalist in the first season, is widely credited as a pioneer behind the early success of UFC following his thrilling back-and-forth three-round clash with season 1 winner Forrest Griffin at TUF Finale on April 9, 2005.

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"Stephan Bonnar was one of the most important fighters to ever compete in the Octagon," the UFC president said.

Former lightweight champion Frankie Edgar commented: "Stephan Bonner a key piece to the growth of our sport. I remember watching him and Forest battling it out and thinking, I gotta try this out. RIP to a true pioneer!"

BJ Penn, another former lightweight champion, added: "RIP Legend."

"Terrible news. One of the nicest guys in MMA," he added in another tweet.

UFC welterweight fighter Michael Chiesa similarly remarked: "My condolences go out to Stephan Bonnar’s family. His fight with Forrest Griffin changed the landscape of the sport of MMA and pushed it to the next level. He’s a big part of the reason we are here today."

UFC flyweight Cody Durden added: "Rest In Peace to the man who helped keep the sport alive! Prayers up for your friends, and family!"

Former Middleweight Champion Michael Bisping also chimed in. As did longtime UFC referee John McCarthy.

In the TUF1 finale, Bonnar and Griffin participated in one of the UFC’s most iconic fights — which forever changed the UFC as a sport and an entertainment venue.

"His fight with Forrest Griffin changed the sport forever, and he will never be forgotten," White said Saturday. "The fans loved him, related to him and he always gave them his best. He will be missed."

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Griffin won the bloody brawl by decision, but both men were awarded UFC contracts for their remarkable performances.

In July 2013, just over eight years after the contest, both fighters were inducted into the Hall of Fame.

"As far as this company goes for sure, but as far as this sport goes—this was the most important fight in the history of this company," White said at the time, according to Bleacher Report.  "At the time when this fight happened, you know where we were back then, and what was happening with the sport. We were $44 million dollars in the hole in this business."

"During six minutes of that fight, 12 million people tuned in. You know how crazy that is? You know what insane numbers those are? There has never been a more important fight in the history of the UFC. There has never been a more important fight than maybe UFC 1 in the history of mixed martial arts," White added at the Hall of Fame ceremony.

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The two men participated in a rematch on Aug. 26, 2006, with Griffin also winning by decision.

Bonnar, who was from Hammond, Indiana, competed in bouts with several former champions, including Griffin, Tito Ortiz, Anderson Silva, Rashad Evans, Jon Jones, Lyoto Machida and Mark Coleman.

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He finished his career with a record of 15 wins and nine losses.

Last month, former UFC veteran Anthony "Rumble" Johnson also passed away following a lengthy battle with an undisclosed illness. 

Fox News' Ryan Morik contributed to this report.