Antagonist
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Character Role Analysis
Voldemort/Malfoy
Okay, okay, Voldemort isn't really in this film, except in flashbacks, but he's always looming large as the foe that Harry needs to conquer (with Dumbledore and all other good wizards behind him). He is the big bad.
We'll give an honorable mention (er, or maybe a dishonorable one?) to Draco Malfoy, though. Draco has been given a nasty secret mission to carry out at Hogwarts (for Voldemort, natch), and Harry spends a lot of time and energy trying to figure out/thwart these plans. We'd say he deserves a nod in the "Antagonist" category, wouldn't you?