Jay Dee “B.J.” Penn (born December 13, 1978) is a retired 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, Middleweight, and Heavyweight divisions. As a former UFC Lightweight Champion and UFC Welterweight Champion, he is only the second fighter 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 unified the UFC Lightweight Championship (against Sean Sherk) to become the division’s first Undisputed Champion; as well as broke the all-time lightweight title defense record. Penn was inducted (as the first lightweight or featherweight and only the second welterweight combatant) into the UFC Hall of Fame, as the inaugural inductee in the Modern-Era Wing by his career-long adversary, Matt Hughes, during International Fight Week in conjunction with UFC 189 in July 2015.
During his reign, Penn holds the distinction of being undefeated as a Lightweight for over eight years, spanning a nine-fight unbeaten streak in the division. 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.