Jay Dee "B.J." Penn (born December 13, 1978 in Kailua, Hawaii) is an American professional mixed martial arts (MMA) fighter and Brazilian Jiu-Jitsu practitioner, currently the UFC Lightweight Champion. 

He holds notable wins over Matt Hughes, Takanori Gomi, Jens Pulver, Caol Uno, Duane Ludwig, Matt Serra, Rodrigo Gracie, Din Thomas, Renzo Gracie and Joe Stevenson. 

He is the first American-born winner of the World Brazilian Jiu-Jitsu Championship (Mundial) in the black belt category (2000), former Ultimate Fighting Championship (UFC) welterweight champion, and was a coach on the The Ultimate Fighter 5 reality show. B.J. became UFC lightweight champion at UFC 80, becoming only the second man after Randy Couture to win UFC titles in two different weight classes.