Jay Dee "B.J." Penn III (born December 13, 1978) is an American professional mixed martial artist and Brazilian Jiu-Jitsu practitioner. Penn competed in the Ultimate Fighting Championship (UFC) and in K-1. Penn was the first American Gold medalist of the World Jiu-Jitsu Championship. In mixed martial arts, Penn has competed in the Featherweight, Lightweight, Welterweight, and Middleweight divisions. A former UFC Lightweight Champion and UFC Welterweight Champion, he is the second of seven fighters in UFC history to win titles in multiple weight classes. Penn was a Co-champion in the UFC 41 Lightweight Tournament, due to an eventual draw with Caol Uno in the tournament finale. Through his tenures as champion, Penn unofficially unified the UFC Lightweight Championship (against Sean Sherk) and broke the all-time lightweight title defense record. In 2015, Penn was made the inaugural inductee into the Modern- Era Wing of the UFC Hall of Fame.Penn was considered one of the top pound-for-pound mixed martial artists in the world early in his career and holds victories over opponents such as Din Thomas, Caol Uno, Paul Creighton, and Matt Serra. Penn won the Rumble on the Rock Lightweight Championship in K-1. He submitted long-reigning then-champion Matt Hughes to capture the UFC Welterweight Championship.Following a period in which Penn competed exclusively for K-1, he returned to the UFC and won the UFC Lightweight Championship. He made a record three subsequent title defenses before losing his title to Frankie Edgar.UFC President, Dana White, credits Penn with bringing the lower weight divisions into the mainstream of mixed martial arts; he describes Penn as "the first crossover pay-per-view star for the Ultimate Fighting Championship's lighter weight divisions", as well as saying that "[through his] accomplishments, B.J. Penn built the 155-pound division".Penn is regarded as one of the greatest fighters in the history of the sport.
He is also known as Jay Dee "B.J." Penn and Jay Dee Penn.