For first-time viewers of Star Wars, when a senile-looking little green alien begins talking to Luke about finding Yoda, there might be a temptation to dismiss the character as being nothing more than a little dose of comic relief in a pretty sombre film. However, when the green guy reveals himself to be the legendary Jedi master that Luke is searching for, he and the audience begin to piece together the point.
Yoda is the encapsulation of what the Light Side of the Force has against the Dark, it doesn't matter what your size, shape or appearance is. Yoda is a brilliantly written character, however one throwaway line in Return of the Jedi opened up a whole world of interesting story lines and arcs that we sadly only get some glimpses at.
When Luke tells Yoda that he's looking tired, the Jedi master retorts back that, when he reaches 900 year old, he won't be looking too hot either. Granted, Luke was a bit busy trying to save the galaxy at that point however, for audience members out there, it opened up our imaginations to a whole world of imagery over what Yoda's incredibly long life might have looked like, even if that is pretty much the only sprinkling of backstory we get for this green good guy.