Who is the sole hero of Julius Caesar?
In several respects, Brutus is the play's only hero. He is developed as one of Shakespeare's tragic heroes (like Macbeth, Hamlet, Lear, and Othello) by fulfilling Shakespeare's conventions for that role. Brutus is an admirable man who falls from great power and is destroyed as the result of a fatal flaw within his own character.
Putting aside these characteristics of the tragic hero, however, Brutus still stands as the play's hero. As Antony points out in the play's conclusion, Brutus acted out of conscience, trying to save freedom in Rome. His motives were honorable, and all his subsequent actions showed his devotion to Rome. He sacrificed his home, his marriage, and his life in doing what he believed was his duty.
Unlike Cassius, once Brutus had an army behind him, he did not abuse his power by profiting from it, making money at the expense of peasants. Unlike Antony, once Brutus had power, he did not cheat (Antony's treatment of Lepidus) or steal from the Roman citizens to enrich himself. (Remember that Antony changed Caesar's will to keep the Roman citizens from the inheritance Caesar had intended for them.)
As for considering Caesar as the play's hero, he is not presented as such in the drama. Caesar had fought bravely in his role as Roman general to protect Rome from enemies and to enlarge its territory, but once he had secured power in Rome, Caesar behaved with arrogance, preserving his power and seeming to seek even more.
Of all the major characters, only Brutus maintained his integrity and acted with courage to achieve what he perceived to be honorable ends.
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