If you are struggling to identify who your protagonist is, consider the following:
- What is the central challenge of your story and whose goal it is to overcome this challenge?
- Who is the antagonist in the story and what character are they blocking the most? Which character has the most to gain from overcoming or defeating the antagonist?
- Who in your story is facing the most difficult decisions?
- Whose decisions and choices tend to lead have significant consequences, either good or bad?
- Who in your story is undergoing some level of personal transformation as a result of the events in the story?
- If you had to all of the characters in your story but one, who would you absolutely have to keep?
Also, remember that your protagonist is not necessarily:
- The person whose point of view the story is told from
- The person who gets the most "screen time"
- The "good person"
Though there are many famous examples (example: Game of Thrones) where there appears to be multiple protagonists - and some romance stories where there are co-protagonists - these tend to be exceptions to the rule. It's often the case that upon close inspection just one of the characters is the true protagonist.