A long time ago...
Such a difficult challenge. Even bypassing the principal characters, there are too many candidates: Salacious B. Crumb, Wedge, Sabine Wren, K-2SO, Malakili (big guy with a big heart).
But if you held a blaster to my head and made me choose, I would opt for the Millenium Falcon. Coolest vehicle in cinematic history, but not technically a character.
So if I’m going to break the rules and put forward a non-character, I’m going to take inspiration from D_Reaper and Uschibear and vote for the sound of Star Wars. Adding to their comments about Artoo’s robo scream and John Williams’ score, I present:
I can no longer hear the 20th Century Fox fanfare without feeling my excitement building.
The silence of ‘A long time ago in a galaxy far, far away…’ before the Star Wars title thunders onto the screen to the rousing der der, duh-duh-duh der der, duh-duh-duh der der, duh-duh-duh der.
The electric buzz of a lightsabre coming to life; and the sharp crackle as it defends a Sith’s sweeping thrust.
The Mos Eisley cantina music. (Did you hear it in Paul?)
The animalistic scream of a TIE fighter flying past.
R2D2 – just about everything the beloved little droid utters. (But I have heard he is the most foul-mouthed character ever, hence every word is bleeped out.)
And finally, the most heartrending sound I have ever heard:
As Han is lowered into the carbon-freezing chamber on Bespin Cloud City, the anguished cry Chewbecca releases. Breaks my heart.