Here's a little movie lesson for the day. A protagonist is the person the audience is rooting for, (hence the word "pro.") Examples include, Luke in Star Wars, Harry Potter in Harry Potter, and Janee Glenn in Girls Just Wanna Have Fun. In Pirates of the Caribbean: Curse of the Black Pearl the protagonist is Will Turner.
"WHAAAAAAAAT?" You ask? "It's not Jack Sparrow?"
No. It's not. If Pirates of the Caribbean were Star Wars, Jack Sparrow would be Han Solo.
So how can you recognize the protagonist? It's easy when you follow these simple steps.
1. First and foremost, the protagonist is the person who changes at the end. (A movie is a "bad" movie, when nobody changes at the end.) Continuing with the Pirates example - at the start of the film, Will Turner won't stand up for himself, but by the end of the movie he's willing to finally fight for what he believes in. (Incidentally, when you answer the question "what made the protagonist change?" You've got the purpose/moral of the movie.) To continue with the Star Wars example - Luke Skywalker first comes on the scene as a whiny, no-nothing complainer, but by the end of the movie he's saving the galaxy. However, Han Solo also goes through a monumental change! (Do you see now why we need more than one step to determine who the protagonist is?) Let's continue.
2. The protagonist leads the action. What happens, happens TO the protagonist.
3. The ANtagonist (AKA: who, or whatever, stands between the protagonist and the protagonist's goal,) is in the protagonist's way. Pirate example - Barbosa kidnaps Elizabeth Swan, which is what drives Will Turner, and thusly the entire plot. Star Wars example - Darth Vader stands between Luke and the freedom of the galaxy. Ah! It's making sense!
5. This one's a no-brainer and not always helpful - When searching for a movie's protagonist, ask yourself which person are you rooting for? Pirate example -When Jack Sparrow and Will Turner are fighting at the beginning, we're on Will's side because he's a nice guy, who isn't a known pirate, and hasn't held a sword to someone's throat in the last half hour. In Star Wars, we're not especially on Leia's side because she's a small character who's side is part of the Luke-side, and while we like Han, he's kind of an unreliable nerfherder.
The battle for protagonistship is the reason why The Prestige is such an amazing movie. The movie starts with the audience on Angier's (Hugh Jackman) side, because that mean ol' Bordon (Christian Bale) killed his wife (Rebecca Hall.) But by the end of the movie we've completely switched sides to Bordon's, because that mean ol' Angier has gone completely nuts in his revenge obsession. (And our favorite plots are the ones about revenge.)