Claudius is the primary antagonist in Hamlet. He thwarts Hamlet by killing his father. And when he usurps the Danish throne, Claudius denies Hamlet the future that rightfully belongs to him. Claudius additionally frustrates Hamlet by marrying his mother, Gertrude. Hamlet and Gertrude previously enjoyed a loving relationship, but her remarriage fatally compromises their bond. Not only must Gertrude divide her loyalties, but Hamlet must also grapple with his disgust at what he considers a traitorous, near-incestuous marriage. Yet despite Hamlet’s frustration with his mother, his chief enemy remains Claudius, who is driven by desire for love and power. Claudius reveals as much during his confession in Act Three, when he admits that he can’t truly repent because he retains possession of the goods that he acquired through sin—that is, Gertrude’s hand and the Danish throne. Unable to repent, Claudius seeks to rid himself of Hamlet instead. In Act Four he sends Hamlet to England with a sealed letter instructing the English king to execute the bearer. When this plan goes awry, Claudius hatches another plot involving Laertes slaying Hamlet with a poisoned-tipped sword. The second plan succeeds, but also results in Claudius’s own death.
As much as Claudius stands in Hamlet’s way, Hamlet also functions as his own antagonist. Hamlet is a student of philosophy, and has learned to master the fine art of careful thinking. Yet Hamlet’s mastery of logic and philosophical speculation has also resulted in a deep indecisiveness that makes it difficult for him to take the steps necessary to avenge his father’s murder. Throughout the play Hamlet remains paralyzed, incapable of breaking free from his own thoughts. For instance, he struggles to determine how he is supposed to feel about his father’s death, and whether or not he can morally justify killing Claudius. He also longs for clear answers to several questions. He wants to know what really happened to his father, and whether or not he can trust Ophelia. He also wants to know what will happen to him when he dies, and whether Claudius will go to Heaven or Hell. Finally, he wants to know why he is so unhappy. Because Hamlet can’t answer any of these questions with certainty, he finds it impossible to decide how to act. In the end, Hamlet’s indecision defeats him, and he goes to his death still uncertain about everything.