Peter Mayhew did not come up with or do the voice of Chewbacca. Lucasfilm sound designer Ben Burtt did, compositing it from grunts and growls from a variety of different animals. Mayhew actually had English lines, which he spoke for the benefit of the actors on set.
Peter brought a charm that I don’t think many people could pull off. Let’s face it: when Star Wars first started, it could easily have fallen off the rails — 70s sci-fi / fantasy has still stuck in the campy mindset of the 50s and 60s (with notable exception of 2001: A Space Odyssey).
Dressing up as a giant Sasquatch with a crossbow could’ve been an utter disaster, but Peter made it work. Actually, strike that: he gave Chewie life.
One of the most interesting aspects of Mr. Mayhew’s work is that the costume was a rather rudimentary one. The face had minimal articulation, so he relied mostly on body language for conveying emotion.