Neither of those, though Vader was portrayed by two actors in the film: David Prowse bodily and James Earl Jones vocally. (RotJ would add a third actor to portray unmasked and ghostly Anakin, of course.)
I was hoping that there had been a stunt guy in there somewhere.
R2 was to be my next guess so...
… actually I've changed my mind. Chewbacca? They might have different people wearing the outfit for closeups and scenes where a smaller actor was required to wear the headpiece of the suit.
"...not having to believe in a thing to be interested in it and not having to explain a thing to appreciate the wonder of it."
Wedge was the pilot in the Death Star attack briefing who expressed doubt that they could hit a two-meter target, to which Luke made his "womp rats" reply. The actor playing Wedge in that scene is named Colin Higgins.
For whatever reason, George Lucas decided to recast Wedge for his remaining scenes. So in Wedge's X-Wing cockpit scenes, he is portrayed by Denis Lawson, who then plays Wedge in the rest of the trilogy.
To sync up Wedge's voice for his lines (and because Lawson has a thick Scottish accent, a third actor, David Ankrum, was used to dub all of Wedge's scenes. Wedge was dubbed again in Empire, but apparently Lawson faked an American accent in RotJ.
I was quite stunned by this when I was doing some research to try to come up with my trivia question! Here's one of the articles I used to fact-check my question, just to make sure they weren't intended to be 2 different characters.
Yeah, I termed this one as odd earlier because you would expect it to be one of the creatures or droids, but it was a just a dude, albeit one of the more well-known ancillary characters in the movies!
I wonder what Colin Higgins thought of being replaced? I just thought it was a different pilot with the earlier lines. It's a busy attack on fhe death star so it didn't seem odd not to see him again. Great question.
"...not having to believe in a thing to be interested in it and not having to explain a thing to appreciate the wonder of it."
I felt a great disturbance in this Trivia Thread, as if millions of voices suddenly cried out their answers and were suddenly silenced by the absence of a question.
Only if a Doozy is a creature encountered in a Tatooine cantina.
The Millennium Falcon, overweight gangsters forcing slaves into metallic bikinis, carbonite frozen heroes and clone armies were all influenced by what other sci-fi source?
"...not having to believe in a thing to be interested in it and not having to explain a thing to appreciate the wonder of it."