Compare Tom and Gatsby

It could be easily and fairly argued that Gatsby is the novel's protagonist - he is, after all, the character driving the action and defining the narrative. Everyone talks about him, everyone reacts to him, everyone places him in the forefront of their consciousness and activities. For himself, he is driven and defined by a single objective (i.e., to claim Daisy Buchanan for himself), again as many traditionally viewed protagonists would be. It could also be argued, however, that he is more of a powerfully effective antagonist than a protagonist, if the term "antagonist" is taken as referring to a character who, by action and/or by attitude, triggers transformation in a protagonist. In Gatsby's case, both his actions and his attitude cause clear, and profound, transformation in the life and perspectives of Nick Carraway. In other words, although he is simultaneously, and perhaps paradoxically, both a vividly portrayed character and an enigma (truths about how he made his money, for example, are never fully revealed), and although his is undeniably the dominant presence in the narrative, he is still the measuring stick by which the transformation in the central character is measured. He is, in short, a catalytic antagonist.

Tom is Daisy's husband, in his own way as self-indulgent and self-righteous as Daisy. He is physically and emotionally violent, unable and/or unwilling to see how his actions and attitudes are harmful to himself and to those around him. Several times, particularly at the novel's conclusion, Nick refers to Tom's attitude of both entitlement and almost delusional self-justification. He is controlling and destructive and as such, he is, like the other main antagonists (Gatsby, Daisy, Jordan) embodiments of a dominant societal attitude in the upper classes of the time in which the novel is set, attitudes which the author seems thematically intent upon condemning. Indeed, the self-serving attitudes of all these characters can ultimately be seen as the core of his (the author's) contemplation on the perversion of the so-called American Dream.