Mark Antony’s personality appears to have undergone a change in Act IV, indicating that his speech at Caesar’s funeral was at least partially a manipulative power grab. He seems quite pleased to have the authority to kill “with a spot.” He can simply mark certain names on a paper, and those people are chosen for death. Perhaps he is happy to take vengeance for Caesar. Whatever the case, he comes across as quite cold and arrogant. When Lepidus says that Antony’s nephew Publius must die, Antony simply replies, “He shall not live.”
This scene also foreshadows the power struggle between Octavius and Antony. Octavius defends Lepidus as a “tried and valiant soldier,” but Antony retorts, “So is my horse, Octavius.” Antony uses the fact that he is older and more experienced than Octavius to support his argument that Lepidus is not fit to rule with them and must only be used “as a property.” Antony clearly views at least some people as nothing more than objects to be controlled.
Mark Antony is quite a multifaceted figure in Julius Caesar. He is initially underestimated as a young man who enjoys sports and revelries. At Caesar’s funeral, it is revealed that he is a master manipulator, and in Act IV, we see that he is even more calculating and unsentimental than he previously appeared.
Personally, my impression of Antony in act 4 is that of someone who has let power go to his head and has forgotten all of the sorrow he felt at Caesar's assassination and his disgust over people like the conspirators. Now that he is part of the triumvirate with Lepidus and Octavius, he has become as power-hungry as the next guy, even looking for ways to rid the triumvirate of Lepidus. It doesn't seem like he's really thinking about what's best for Rome - rather, it's become what is best for Antony. In speaking of Lepidus, Antony says to Octavius:
"This is a slight unmeritable man,
Meet to be sent on errands. Is it fit,
The threefold world divided, he should stand
One of the three to share it?"
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