Michael Reeves' final film, shot September 18-November 13 1967. One year later, Reeves was replaced by Gordon Hessler on "The Oblong Box," and died early in 1969.
Vincent Price regarded his performance here as the finest of his horror movie career.
Paul Ferris, who wrote the film's dramatic music score, also acted in the movie under the pseudonym Morris Jar as a homage to film composer Maurice Jarre.
A completely new score was written for the US video release by Kendall Schmidt.
Director Michael Reeves wanted Donald Pleasence to play Matthew Hopkins, but AIP, the American distributor and co-financier of the film, insisted that Vincent Price play the title character, and Reeves grudgingly accepted.
On the first day of filming, Vincent Price fell from his horse. Director Michael Reeves refused to see him, hoping that angering Price would help the actor make his character more fierce.