Kix is the 501st Legion's field medic. StarWars.com's databank records the inscription on his helmet — "a good droid is a dead one" — and notes that he "remained combat-ready" despite a job defined by saving rather than taking lives. He is voiced by Dee Bradley Baker.
He is the clearest counter-example to the idea that the clones were interchangeable: an identical man who chose a specialism that keeps the others alive, in an army designed on the assumption that they were replaceable.
Catalogue entry. This figure has a verified record here rather than a full write-up — the encyclopedia labels its own depth instead of padding it.