The voice of Darth Vader, provided by James Earl Jones, is one of the most iconic aspects of Star Wars. But James Earl Jones wasn't in that outfit—it was British actor David Prowse, who was cast in part because he was huge (reportedly 6'5" and a former body-building champion).

George Lucas always intended to replace Prowse's voice, but it's a bit of a shock to hear a muffled British voice coming out of Darth Vader's helmet. Here's video showing what Darth Vader sounded like on the set before James Earl Jones re-recorded the dialogue:

(Via Devour.)