Jay Dee "B.J." Penn III (born December 13, 1978) is an American professional mixed martial artist and Brazilian Jiu-Jitsu practitioner. Penn debuted and competed in the Ultimate Fighting Championship (UFC), and later in K-1. Prior to fighting for the UFC, he became 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. As a former UFC Lightweight Champion and UFC Welterweight Champion, he is the second of only five fighters in UFC history to win titles in multiple weight classes. Penn was also a Co-champion in the UFC 41 Lightweight Tournament, due to an eventual draw opposite 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. Penn was inducted into the UFC Hall of Fame, as the inaugural inductee in the Modern-Era Wing by career-long rival Matt Hughes, during International Fight Week in July 2015.He emerged as one of the top pound-for-pound mixed martial artists in the world early in his career (a recognition he would hold until his initial retirement from the sport), defeating opponents that included Din Thomas, Caol Uno, Paul Creighton, and Matt Serra. Penn soon-after secured his initial world title with K-1, submitting Takanori Gomi for the Rumble on the Rock Lightweight Championship. He immediately ascended into the Welterweight division of the Ultimate Fighting Championship, submitting long-reigning then-champion Matt Hughes to capture the UFC Welterweight Championship, which was eventually relinquished due to contract disputes.Penn therefore departed from the promotion to compete exclusively for K-1. He submitted Duane Ludwig and defeated Rodrigo Gracie and Renzo Gracie before eventually re-signing with the Ultimate Fighting Championship. Following contentious losses to Georges St-Pierre and Matt Hughes, Penn returned to the Lightweight division to submit both Jens Pulver and Joe Stevenson en route to claiming the vacant UFC Lightweight Championship. He made a record three subsequent title defenses; defeating uncrowned champion Sean Sherk and challengers Kenny Florian and Diego Sanchez before losing his title to Frankie Edgar in a disputed decision.
In the sunset of his career, Penn returned as a Welterweight to successfully complete his trilogy with Matt Hughes, before retiring between two losses and a draw in attempts to regain the UFC Welterweight Championship. In pursuit of a career resurgence with a descent into the Featherweight division, Penn conclusively announced his retirement following another loss to Frankie Edgar. Penn ends his UFC Career with 7 straight losses, the most straight losses in UFC history.
UFC President Dana White credits Penn as the man who brought the lower weight divisions into the mainstream of mixed martial arts; claiming Penn to be "the first crossover pay-per-view star for the Ultimate Fighting Championship's lighter weight divisions", as well as that "[through his] accomplishments, B.J. Penn built the 155-pound division". Credited as the greatest Lightweight combatant in mixed martial arts history, Penn's domination of the division, as well as his performances in higher weight classes have him 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.