Criteria: TOS Crew. Not main cast. Impact beyond one episode.
That leaves out some notable names like Nurse Chapel, who is basically a main character at times, and episode-centric characters like Bailey and Stiles. It also leaves out non-crew like Charlie Evans and Sarek, and of course:
The obvious #1 pick here is Khan Noonien Singh. Long before the current stewards bludgeoned the character through overuse, Khan was already a genuine pop culture icon, rivaling the popularity of Kirk and Spock among non-nerds.
I admit this is a bit of a no-brainer, especially since she was originally supposed to be more than a minor character, but Rand had a resurgence in the movie era and even came face-to-face with Janeway… kinda.
The crew of redshirts who ran the ship often featured recurring faces — for obvious reasons — but few of them got elevated to minor character status. Lt. (and later Commander) Kyle is one of the most prominent background faces to become an actual character. Kyle was a transporter chief, helmsman, and later communications officer of the Reliant.