David Prowse played Darth Vader on screen for most of the original trilogy, with the exception of lightsaber duels, which were done by stuntmen. Of course Darth Vader was voiced by James Earl Jones. A wise decision if you’ve ever seen video of Prowse saying Vader’s lines during filming (it’s kinda the Mike Tyson/Brock Lesnar syndrome). As @ucme said, Sebastian Shaw played the unmasked Vader and Vader/Anakin’s ghost in the original version of Return of the Jedi. Replacing the ghost with Hayden Christensen makes a certain sense. Why wouldn’t Vader/Anakin’s ghost revert to how Anakin was before he became corrupted? Also Hayden Christensen played Darth Vader in that brief scene towards the end of Revenge of the Sith where the “reborn”, fully suited Vader is seen for the first time (chronologically speaking of course).