Jeffrey “Duke” Roufus, a former kickboxer and MMA coach to legendary fighters, has passed away at 55.

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Roufus died peacefully in his sleep on Friday, according to business partner Scott Joffe.

“Duke was more than a celebrated trainer and champion kickboxer — he was a mentor, innovator, father and friend whose influence transformed the landscape of mixed martial arts,” Joffe wrote Friday on Facebook.

“His knowledge, charisma, and passion inspired countless fighters to reach heights they never imagined possible,” Joffe, who was a business partner with Roufus for nearly 30 years, continued. “From world champions to first-day students, everyone who crossed his path felt his genuine care and unwavering belief in their potential. His loss leaves an irreplaceable void in the sports and in the hearts of all who knew him.”

Jeffrey “Duke” Roufus was a Champion Kickboxer Before Becoming a Top MMA Coach

Roufus began his kickboxing career in the 1990s, compiling a 36-8-1 record and winning eight titles. His final title, the I.K.F. world super heavyweight championship, came in 1998. He won his last fight in 2008, per MMA Fighting.

Roufus shifted to coaching and founded the Roufusport MMA Academy. His roster of successful clients includes former UFC champions Anthony Pettis and Ben Askren, as well as WWE star and former MMA fighter CM Punk.

“When my dad was killed, you took me in and became my father…. Together we did the impossible and made it to the top!” Pettis wrote on Instagram on Friday. “I will always make you proud. You’ve taught me so much. I will make sure your legacy continues on.”

mma-legend-duke-roufus-dead-at-55-training.jpegAnthony Pettis spars with coach Duke Roufus during an open workout for media and fans at the Hyatt Regency Vancouver on August 25, 2016. (Photo by Jeff Bottari/Zuffa LLC/Zuffa LLC via Getty Images)

“The measure of a man is not in what he says or does in life, but in what others say of him after he’s gone. Rest in Paradise, my friend,” Joffe wrote alongside an Instagram collage on Saturday. “We accomplished many, many great things together and helped countless people change their lives for the better. As I always told you, thank you for blessing me with the opportunity to be part of your life and accomplishments. We soldier on together with one goal in mind, to continue to bring victory and honor to the Roufus name.”

Roufus is survived by his wife, Tami, and his daughter, Lula.