Jayne Cobb

Jayne Cobb is the muscle on Serenity, a mercenary who joined the crew for money and stays for reasons he'd never admit. He's mercenary in the literal sense — loyalty is negotiable, self-interest is not — and he says so, loudly, armed to the teeth and proud of it.

The joke is that Jayne is written as pure venal self-interest, and the show keeps letting him surprise you anyway. Adam Baldwin plays the thuggishness completely straight, no wink, which is exactly why the flashes of decency underneath land as funny instead of soft.