Even though Prince Prospero is the Protagonist, he isn't necessarily the "good guy." Why is he still considered the protagonist?

Hey guys! for my reading class we have to write a review about a movie that we ourselves can pick. i picked the movie the boy with striped pajamas. so if you could let a couple bullet points below i am willing to give you 20 points more than 10 bullet points about the movie and inserting facts and whats its about. plz by this week