The actor was James Earl Jones.

David Prowse was the actor and James Earl Jones was the voice

Peter Diamond was the stunt co-ordinator for the original three Star Wars, he did not appear as Darth Vader. Diamond did the stunts as the Tusken Raider who attacked Luke in A New Hope, a Biker Scout in Return of the Jedi and was 1 of 3 stunt men as stormtroopers in other action scenes. He also appeared in cameos as Garouf Lafoe; the character who gave Obi-Wan and Luke away to the Stormtroopers in Mos Eisley and as Corporal Prescott; one of the Death Star detention block guards. Vader's stuntman/duelist was swordmaster Bob Anderson in the two sequels. So, counting stuntman Anderson, but stuntmen are rarely given screen credit as characters, Vader has the distinction of being the only character to be portrayed by 4 actors at the same time. http://www.blueharvest.net/scoops/peter.shtml Here's some stuff on David Prowse, Vader's body; many times weightlifting champion in Britain, Trained Christopher Reeve for his role as Superman, awarded the M.B.E. (Member of the British Empire) in the 2000 Queen's Millennium Honours List ( which means he is legally entitled to be called MISTER Prowse), barred from doing the lightsaber duels because in first movie he kept breaking the poles that stood in for the lasers, offered role of Chewbacca but chose Vader "... because everyone remembers the villain," unaware that his voice dubbed by James Earl Jones' until he saw the movie, and has never even met Jones. http://www.imdb.com/name/nm0001190/bio

in episode 3 the guy who plays the role of anakin begged george lucas to also let him play as darth vader when anakin becomes vader in episode 3, he got the role but james earl jones did the voice of vader once again