Julius Caesar is ambitious and shows tendencies toward tyranny. He is a strong military and civic leader whose reforms have benefited Rome, but many senators fear he will keep the Romans enslaved to his whims. His inflexibility, even in the face of death, causes conflict with those who want to protect him.
Brutus is the play's tragic hero. His moral conflicts provide the main ethical dilemma of the play. He is manipulated by Cassius into agreeing to take part in the plot to assassinate his friend Caesar. Brutus is the last person to participate in the attack, and his wound is the one that finishes the act. Caesar seems hurt more by Brutus's betrayal than by the wound itself. The play's other characters, even Brutus's enemies, respect his loyalty and wisdom.
Cassius is devious and cunning. His morality is primarily practical, and he makes tough moral decisions based on whatever will lead to the best outcome for himself—killing a leader or protecting greedy officials. He's also choleric, or easily angered. Honor and loyalty have meaning to Cassius, though, which he shows by releasing his slave Pindarus on the battlefield.
Antony is first shown to be a devoted follower of Caesar who has little power himself. As the play progresses to its climax, the audience realizes that Antony has been hiding his true skills as a speaker, tactician, and soldier. His bid for power is successful because he's willing to undertake daring political moves. He is emotional and passionate.
Octavius is Julius Caesar's great-nephew and is a skilled soldier. Following the assassination he seeks vengeance for Caesar's death. Octavius doesn't have Antony's way with words or gift for long-term planning, but he has Caesar's political acumen and respect for ritual. With Antony and Lepidus, he forms the new triumvirate that leads Rome.