When George Lucas began working on Star Wars, he approached Ben Burtt, a former classmate at the University of Southern California, for help. Burtt, a professional sound designer, knew how sound effects could subtly shape a story and make a fantasy universe seem real.
Burtt developed the sounds of Star Wars that are now instantly recognizable, including that of the lightsaber, the TIE fighter engine, Darth Vader's breathing, blasters, and R2-D2's beeps and chirps. This task involved a surprising amount of work. For example, to prepare Chewbacca's voice, Burtt recorded several different animals at optimal times and then combined their intonations:
"Mostly bears, with a dash of walrus, dog, and lion thrown in," Burtt once said simply when asked how he found the sounds to create the character of Chewbacca's voice. But it took some doing: Burtt would travel to oceanariums on the off chance that their walruses would give him just the right sound. As he would later recall about visiting Long Beach's Marineland of the Pacific, which closed down in 1987, "Its pool had been drained for cleaning—the walrus was stranded at the bottom, moaning—and that was the sound!"
You can learn more about 6 iconic Star Wars sound effects at Popular Mechanics.
-via Jonah Goldberg
Maybe the article mentions it, but Burtt played the Imperial officer in Return of the Jedi who gets hit in the face by Han Solo and falls over a railing. He does an imitation of the famous Wilhelm Scream on his way down.