Lucy had Ethel, Batman had Robin, Marshall Dillon had Chester and Festus.
Every good hero needs a sidekick. The sidekick may not be too bright, might not be real good in a fight, but he/she is always loyal. Sometimes (Rhoda Morganstern) the sidekick gets the best lines, but never the guy/girl.
So who’s the best sidekick. We’ll arbitrarily have one winner for TV, and another for movies.
My choice is clear. Good in a fight, stayed in the background but always there, sometimes provided a little comic relief. It has to be R2D2.