That Marc Antony is a clever man who is also expedient is evident from the first act. For, in Scene 2, Casca describes for Brutus how on the Feast of Lupercal, on a street in Rome after Caesar has returns to Rome as the most powerful man in the Republic there is a procession, and Marc Antony places a coronet of victory upon Caesar's head, but Caesar feigns his refusal of it. However, when Antony replaces the coronet, Casca says, "...to my thinking, he was very loath to lay his fingers off it" (1.2.247).
So, Marc Antony exhibits certain opportunistic traits since the advancement of Caesar to emperor would have also advanced him. Therefore, after Caesar is assassinated, Antony is aggrieved because he has loved Caesar, but he is also angry that his friend and mentor,has died; surreptitiously, then, he plans his revenge against Brutus and the other conspirators. So, feigning a conciliatory demeanor, he sends his servant with a message requesting that he may be granted permission to speak with Brutus. The servant asks,
If Brutus will vouchsafe that Antony
May safely come to him and be resolved
How Caesar hath deserved to lie in death...(3.1.130-133)
Using the reason that he wishes to know what Caesar has done to deserve death, Antony will then tell the conspirators that he himself is ready to die,
I do beseech ye, if you bear me hard.
Now, whilst your purpled hands do reek and smoke,
Fulfill your pleasure.
Antony requests that the conspirators kill him, but Brutus refuses, "O Antony, beg not your death of us!" He tells Antony that he and the other conspirators receive him with "all kind love, good thoughts, and reverence" (3.1.176). Nevertheless, Antony plans his revenge after he looks upon the corpse of his beloved Caesar:
And Caesar's spirit, ranging for revenge,
With Ate by his side come hot from hell,
Shall in these confines with a monarch's voice
Cry "Havoc," and let slip the dogs of war. (3.1.290-293)
After Marc Antony meets with the conspirators, he requests if they plan to kill him, to kill him now. Since his death would be honorable as he would die next to Caesar. Although, the conspirators assure Marc Antony that he is safe, and no harm would come to him.
After Julius Caesar's death, the conspirators are looking over the body. That is when Marc Antony comes in and requests the conspirators to a. have alone time with him and to b. be able to speak during the public funeral in behalf of the people since he loved Caesar. He also requests for the conspirators to kill him but they don't and see this as a sign that he isn't dangerous. Afterward (in the funeral) clever Antony does actually DOES speak in behalf of Caesar and literally makes the crowd go against Brutus and the conspirators. His speech is downgrading Brutus by sarcastically calling him "an honorable man."