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.

Dux worked as a fight choreographer for Bloodsport, Lionheart (1990) and Only the Strong (1993). He detailed his alleged work for the CIA in the book The Secret Man in 1996, and that same year co-wrote the story for the film The Quest alongside Jean-Claude Van Damme. He sued Van Damme for breach of contract over the film, but lost the suit in 1998. He also lost a lawsuit against Soldier of Fortune for libel the following year, over their claims he had falsified his military and CIA service.

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