Jay Dee "B.J." Penn (born December 13, 1978 in Kailua, Hawaii) is an American professional mixed martial arts fighter and Brazilian Jiu-Jitsu practitioner who is currently the Ultimate Fighting Championship Lightweight Champion.
In 2000, he became the first American-born winner of the World Jiu-Jitsu Championship in the black belt category. Penn is also the former UFC welterweight champion and was a coach on the The Ultimate Fighter 5 reality show. After winning the lightweight title at UFC 80, he became the second fighter (after Randy Couture) to win UFC titles in two different weight classes. He is currently ranked by Sherdog as the #1 Lightweight fighter in the world.
B.J. Penn recently told Fighters Club TV that he would face the winner of UFC 87 Welterweight title fight between Georges St. Pierre and Jon Fitch, which St. Pierre ended up winning by unanimous decision. This fight is now scheduled for January 31 2009, the "UFC Super Bowl Weekend", and is hoped to be the biggest UFC PPV ever.
Prior to the fight with George St. Pierre, B.J. Penn has made a controversial comment, stating that he is going to try and kill Georges St. Pierre in the ring but has later explained that he meant that figuratively.