Antagonist
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Character Role Analysis
Tommy Tammisimo, Ghosts, Vincent
Tommy doesn't have much screen time (which we're sure he's unhappy about), but he's probably the closest thing the film has to a single antagonist. He's mean to Cole and obnoxious to pretty much everyone else. He fits the bill.
However, you could also say that the ghosts that follow Cole around and make his life more difficult are the real antagonists. Of course, we later learn that they're just misunderstood and need some attention to start behaving better. For most of the film, though, they terrorize Cole and obstruct his efforts to live a normal life.
Then there's poor Vincent, who kills our protagonist at the very beginning of the film—that's a pretty antagonist-type thing to do. However, he did that because he was completely tormented his entire life, so it's kind of hard to cast him as a total villain. But he did kill the protagonist...really, it's a tough call. What do you think?