Why does Darth Vader breathe so heavily?

While fighting Ben Kenobi on Mustafar, Anakin Skywalker breathed in the lava and soot from the area where he was eventually struck down and lost his lower legs. read more

Behind-the-scenes explanation: George Lucas wanted Vader to have some menacing auditory quality, so he gave Vader a hermetically-sealed space suit complete with helmet and body armor, which would make some kind of ghastly, horrific, exaggerated, trademark breathing sound. read more

I had wanted to do that and tie it in with the dialogue. It was a nice touch, because it adds to the bogyman quality of the character. Ben had a lot of work in that too. read more