Marvin, who was at the height of his career in 1967 (having just come off a Best Actor Oscar win a year earlier for Cat Ballou), accepted the part eagerly.
Credit three people mainly with the film's success: E.M. Nathanson for his novel on which the movie is based (screenplay by Nunnally Johnson and Lukas Heller), Nathanson saying that while it was fiction, he was inspired by legends of such things actually taking place; director Robert Aldrich, an old hand at action thrillers with movies like "Kiss Me Deadly," "What Ever Happened to Baby Jane?," "The Flight of the Phoenix," "Emperor of the North," and "The Longest Yard" to his credit; and Lee Marvin, a former Marine riding high as an Oscar winner for "Cat Ballou" two years earlier and "Point Blank" the same year.