It's a given that the same actor will play Rudolph and Rassendyll.
Ronald Colman in the lead role in the 1937 film. This was one of Ron's specialties; he'd been playing dual roles of one sort or another since his silent film days.
Completely Different Title: For some strange reason the 1952 film is "Im Schatten der Krone" ("In the Shadow of the Crown") in German, while the title of the book and 1937 film are directly translated as "Der Gefangene von Zenda".
Creator Backlash: David O Selznick was unhappy with the 1937 version, especially the action scenes.
Playing Against Type: As noted below, Douglas Fairbanks Jr plays the villainous Rupert. He had wanted to play both the leads instead.
Fay Wray screen tested for Flavia in the 1937 film. Douglas Fairbanks Jr held onto the clips of this and they survive in the Motion Picture Academy's archive.
David O. Selznick considered adapting Rupert of Hentzau after the success of the 1937 film.
General Trivia:
Two stars of the 1937 version, David Niven and Douglas Fairbanks Jr., took their swashbuckling to Real Life in World War II. Both served in elite units (Niven in the Commandos, Fairbanks in the U.S. Navy Beach Jumpers) both saw combat and both were highly decorated for their actions.
By this point in his career, Ronald Colman had played so many double roles that he was fed up with them (and had, in fact, refused to do so for A Tale of Two Cities). On the other hand, the King's role is tiny and Rudolf Rassendyll gets most of the action.
Reportedly Douglas Fairbanks, Jr. was extremely reluctant to play a villain, but after he allowed himself to be talked into it he turned in a bravura performance that literally makes the film.
