In 1939, Batman first appeared. During that year, Batman was on his own. The next year, Batman was given a sidekick, Robin, the boy wonder. Robin quickly became a prominent character in the Batman franchise. Robin didn't appear in either of the Batman films directed by Tim Burton. There were plans to have Robin in the 1st film, but he ended up being cut out. History repeated itself with the 2nd film. Robin doesn't appear in Batman V Superman or Justice League, because he was murdered by the Joker, offscreen.
Here's a list of the actors who have played Robin in live action: