Tom Buchanan is the main antagonist in The Great Gatsby. An aggressive and physically imposing man, Tom represents the biggest obstacle standing between Gatsby and Daisy’s reunion. For much of the novel Tom exists only as an idea in Gatsby’s mind. In fact, the reader meets Tom long before Gatsby does, and understands that Tom will not back down from Daisy gracefully. Tom’s own adultery would seem to make it easier for Gatsby to steal Daisy away, but Tom maintains a strong need to keep order among his possessions—including his women. Tom is also deeply invested in maintaining the social order. He feels threatened by the idea of the lower classes encroaching on his privileged life. He objects to Gatsby not only because Gatsby is in love with Daisy, but also because Gatsby comes from a poor background. When he says Daisy wouldn’t leave him “for a common swindler who’d have to steal the ring he put on her finger,” he implies that he’d understand Daisy leaving him for another wealthy man, but can’t accept her betraying him with someone of lower status. Tom’s antagonism, then, is not just an attempt to thwart Gatsby in his specific quest, but to fight against class mobility in general.
While Tom most clearly stands in the way of Gatsby’s love for Daisy, Daisy herself functions as an antagonist as well. Years prior to the events of the novel, when Gatsby left to join the war effort, Daisy decided to give up on her love for Gatsby and run with a fast and rich crowd. Her decision to marry Tom widened the social gap between Daisy and Gatsby, thwarting Gatsby in his quest to be with her. Even once Tom learns about Daisy and Gatsby’s affair, Daisy prevents Gatsby from attaining his goal of being with her when she refuses to say she never loved Tom. Like Tom, Daisy is deeply attached to her upper class lifestyle. After the accident, even though Gatsby takes responsibility for Myrtle’s death, Daisy once again chooses Tom over Gatsby. All that Gatsby wants is Daisy, but Daisy repeatedly prevents him from attaining this goal of possessing her completely. Even though she loves him, Daisy plays a crucial role in Gatsby’s downfall.
Daisy’s passive role in Gatsby’s death signals a broader, more abstract antagonist that also haunts the novel: the American Dream of upward mobility. All of the characters in the book—even Nick, as he discloses in the opening pages—seek financial improvement in the hopes of securing a better life. Yet none of these characters achieves anything like happiness. Nick is the book’s most astute commentator on the illusory nature of the American Dream. On the novel’s final page, Nick specifically addresses what he considers the elusive nature of the American Dream. Even though hopeful dreaming like Gatsby’s seems to be oriented toward the future, Nick claims that such dreaming is stuck in the past. More specifically, he argues that the American Dream hearkens back to the time before America was even born, when it existed purely as an idea in some Dutch sailors’ minds. Nick’s point is that reality always falls short of the dream, and so striving to stay in the dream can just as easily lead one into a nightmare.