Everybody knows that David Prowse played Darth Vader in the old Star Wars episodes. He was a weightlifting champion and a bodybuilder.
Does anybody know who and why actually chose him to play this important role?
I don't know who chose him, probably a combination of the casting director and Lucas.
David Prowse was tall and imposing and the movie sets that the character appears in were shot in the UK, and he is English.
He did a series of short road-safety 'adverts' in the UK in the 70's - he was the "Green Cross Code Man" - where he had to wear a super-hero costume, stand tall, make obvious body-movements and gestures to teach kids to cross the road. Perhaps this role whilst not 'serious acting' as some people would see it showed Lucas that he had the skills to carry out the role of the expressionless Vader.
As for 'the important role' it was clear from the outset that they planned to dub another voice onto the character (have you heard David Prowse speak? - he has a regional west-country accent) - so what they needed was someone with that physical presence, with some acting experience, and who would not be too expensive.
In 1971, Stanley Kubrick cast him as Julian, the bodyguard of Mr. Alexander for A Clockwork Orange. And when such a great director casts you, it is a big thing. So for Star Wars, he did not even have an audition, George Lucas wanted him to have a role.
It is also said that George Lucas gave him a choice whether he wants to play Chewbacca or Darth Vader.
All they needed was a tall actor.
Since his face would not be seen, behind Vader's mask, and his character's voice would be dubbed by another actor, all that was required was height.
Several actors were perfectly qualified for the part. Dave Prowse was well known in the British film industry, because of his role in Stanley Kubrick's 'A Clockwork Orange', which was entirely filmed in England, and from his role as the Green Cross Code man in tv and cinema road safety adverts, filmed on behalf of the Central Office of Information, a public body.
He had played a lot of stunt work in films and on tv, including science fiction, having had a role in 'Doctor Who', in 1972, as the Minotaur in the serial 'The Time Monster', a role in which he also wore a face mask and had no dialogue.
Also in contention was the 7 foot tall Richard Keil, who, also in 1977, was cast in the Bond film 'The Spy Who Loved Me', which was made in studios in England and on location in Egypt. Keil played 'Jaws', the enormously tall professional assassin, a role that he later repeated in a second Bond film, 'Moonraker', in 1979. Again, it was a part without any dialogue.
One might bear in mind also Peter Mayhew, who was cast in 'Star Wars' as Chewbacca, who also had the requisit characteristics of height and an ability to act despite being entirely concealled within a costume and mask.
So the casting of Dave Prowse as Darth Vader was not entirely a forgone conclusion. There were other tall actors suitable for the part, who were working in England in 1977.