<P> Penn has had two daughters with the same mother . He says that they have never married and "it doesn't matter that much in Hawaii ." Penn is the co-author of Mixed Martial Arts: The Book of Knowledge, an instructional book on mixed martial arts fighting . Penn, along with Dave Weintraub, authored the autobiography Why I Fight: The Belt is Just an Accessory in 2010 . The book debuted at #22 on the New York Times bestseller list . Penn also appeared in the film Never Surrender in 2009 . </P> <P> Since his debut in the Ultimate Fighting Championship, Penn emerged as one of the biggest stars in the history of the sport, headlining a total of eleven main - events (nine pay - per - view main - events) for the UFC during the course of his career (in addition to five for K - 1). Penn was regarded as one of the most controversial and outspoken players in the history of mixed martial arts whose influence was considered instrumental in popularizing the UFC around the world in the 2000s and 2010s . His impact on the sport went beyond his UFC titles and dominant performances inside the octagon . A longtime advocate for drug testing in the sport, Penn was also the first to introduce an independent foundation in MMA to promote, coordinate and monitor the fight against performance enhancing drugs in sports with the inclusion of Voluntary Anti-Doping Association (VADA) during his and his opponent's training camps . </P> <P> Recognized for his role in the resurgence of the lightweight division, Penn is considered to have been the division's most influential figure, turning the weight class around (in bouts with Sean Sherk, Kenny Florian, Diego Sanchez, Jens Pulver, and Joe Stevenson) to become one of the UFC's most popular, at a time when they had considered disbanding the division altogether and many publications had questioned whether lighter - weights could be successful . His nickname, The Prodigy originates prior to him competing in mixed martial arts, from accomplishing his extraordinary feat in the sport of Brazilian Jiu Jitsu (earning his black belt in just under three years and winning the black belt division in the World Jiu - Jitsu Championship only three weeks later). His biography on the UFC website expressed this accomplishment as "an astonishing achievement in a sport where it takes the average athlete ten years or more to reach black belt status . </P> <P> The Ultimate Fighting Championship's inaugural signature gym located in Honolulu, Hawaii,' UFC Gym BJ Penn' is named in Penn's honor . The gym has grown to become one of the largest and most successful in the state of Hawaii . Penn (in his knockout victory over former UFC Lightweight Champion Sean Sherk) is featured in the UFC "Evolution" pay - per - view introduction . </P>

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