I recently listed some protagonists and antagonists from my writing. You may have noticed that the protagonists have the longer character descriptions. However, I think that writers' antagonists should be as richly developed as their protagonists.
How do I reconcile the last two sentences in the previous paragraph. I withheld more about the antoganists, so as not to kill the suspense. In fact, I withheld some information about the protagonists to preserve some suspense.
Though we usually think of the protagonist as "the good guy," sometimes the protagonist is not so good. The protagonist is the character who is the most changed by the events of the story.
Taken as a whole, who is the protagonist of the first Star Wars trilogy? The person who undergoes the most change over the three films is the guy who is usually credited as the chief bad guy--Darth Vader. Star Wars is Vader's quest, and Luke serves as his guide for the quest.