Green Alien

A nameless extraterrestrial glimpsed in passing during one of the show's countless dimension-hopping detours, the Green Alien exists to fill out a spaceport, a bar, or a holding cell — one more inhabitant of the vast, indifferent cosmos Rick drags Morty through. It reacts, complains, or gawks, then vanishes.

It works because it doesn't need to work hard: Justin Roiland tosses off a voice, a grunt, a bit of alien sass, and moves on, and that throwaway quality is the joke. Rick and Morty's universe feels infinite precisely because characters like this exist just long enough to prove nothing here matters much.