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Antony is a good friend of Julius Caesar who launches himself into a major position of power over the course of the play. And, yes, this is the same Mark Antony who has a torrid love affair with Cleopatra and goes down in another Shakespeare play, Antony and Cleopatra.
When we first meet him, Antony is running around in a goatskin loincloth at the Feast of the Lupercal, agreeing to everything Caesar has to say (1.2). After being ordered to touch Calphurnia with the magic fertility whip (head over to "Symbolism" for more on this), Antony declares "When Caesar says 'do this,' it is perform'd."(1.2). By asserting that Julius Caesar's words are authoritative enough to make anything happen, Antony draws our attention to the sheer power of language in the play.
Antony's strong suit is rhetoric (the art of speaking persuasively), which makes him a terrific politician. After Caesar's death, Antony manages to convince the conspirators that he should be allowed to speak at Caesar's funeral. In the famous speech that begins, "Friends, Romans, countrymen, lend me your ears" (3.2.82), Antony delivers a carefully crafted eulogy that's designed to turn the people against the conspirators and launch him into a position of power. The success of Antony's speech suggests that effective leadership goes hand in hand with rhetoric because, after Antony finishes talking, all hell breaks loose and civil war ensues, which is exactly what Antony intended.