DEFINITION:
Protagonist: A protagonist is the character that helps keep the story moving. They usually have a goal or mission to achieve, in which the movie is based about their journey to achieve that goal. In modern times they may also be sometimes called the 'good guy'.
Antagonist: The antagonist is the one that tries to stop the protagonist. As opposed to the protagonist, he is the 'baddie', an obstacle trying to stop from the story progressing.
