In June, 1979, Starlog (tagline: “The Magazine of the Future”) ran an interview with Dave Prowse, the massive British actor who played Darth Vader in Star Wars IV (“A New Hope”). This interview was done before much production had begun on Star Wars V, “The Empire Strikes Back.” During the interview, one of Prowse’s answers seems particularly naïve, especially in retrospect.
Starlog: Have they signed you up for any of the future Star Wars sequels?
Prowse: They’ve offered me Star Wars II and III. As you probably know, Star Wars I, II, and III are actually the fourth, fifth and sixth in the Empire’s chronology. And then they’re going back to do the first three. I’ll do the fifth and sixth, but I probably miss the first because they’ll be going back in Empire history. Then I’ll likely do the second and third. So I could be Star Warsing for the next…10 years?
In fact, Prowse played Darth Vader in the next three movies, but due to production conflicts on both V and VI, the first three movies took nearly 7 years to complete. After that, Lucas backed off Star Wars, and Prowse was not in any of the prequels. It's also notable that he thought the next five movies could be produced so quickly. To compare, the James Bond films of the 60's were released almost on a yearly basis.
Although Prowse can be seen in many movies, such as A Clockwork Orange, and as the monster in Frankenstein and the Monster from Hell, his face never appeared in the Star Wars movies.
According to IMDB, when Sebastian Shaw was revealed in Star Wars: Episode VI - Return of the Jedi (1983) as the "man behind Darth Vader's mask", Darth Vader became the first recurring role in a movie series to be played by three actors at the same time: body by Prowse, voice by James Earl Jones and face by Sebastian Shaw.
Here's the full interview from Starlog, 1979.