Bonnar, who was inducted into the UFC Hall of Fame, died on December 22 of what are believed to be heart-related issues, according to mmafighting.com.
The American went by the nickname "American Psycho" and competed in light heavyweight.
"Stephan Bonnar was one of the most important fighters to ever compete in the Octagon.
His fight with Forrest Griffin (2005 and 2006) changed the sport forever, and he will never be forgotten.
The fans loved him, connected with him and he always gave them his best.
He will be missed," writes UFC president Dana White in a press release.