Frank William Dux (born April 6, 1956) is a Canadian-American martial artist, fight choreographer and author. According to Dux, a ninjutsu expert named Senzo Tanaka trained him as a ninja when he was a teenager.

He established his own school of ninjutsu called Dux Ryu Ninjutsu, and has said he won a secret martial arts tournament called the Kumite in 1975. His alleged victory at the Kumite served as the inspiration for the 1988 film Bloodsport starring Jean-Claude Van Damme. Dux's victory at the Kumite has been disputed, as has the existence of both the Kumite he described and Senzo Tanaka.