" Anything that interferes with the protagonist reaching her goal and fulfilling her unmet desire is the antagonist. That means it might not always be another person. It could be a storm or a demon or a dog. It might be the protagonist’s past or her unfulfilled dreams or her grudge against her friend. Since the antagonist isn’t always a human being, some story theorists refer to the “forces of antagonism” in a broad sense, rather than “antagonist” in a narrow sense. "

― Steven James , Story Trumps Structure: How to Write Unforgettable Fiction by Breaking the Rules