From Shakespeare's Julius Caesar, Antony's speech in Act 3.2 is famous for many reasons, such as its effectiveness in the play, its snatching of almost certain victory from the conspirators, its presentation by Marlon Brando in a movie version, etc.
Essentially, though, it has probably gained such fame because it's so clever with its use of irony.
Antony promises Brutus that he will say nothing negative about Brutus or the other conspirators, so that Brutus will allow him to speak at Caesar's funeral. Yet, Antony is still able to give a speech that turns the crowd into a rioting mob intent on killing the conspirators.
He does this with irony. He uses a refrain of "Brutus is an honorable man," or something similar. Here's how he uses it:
- He tells the crowd that Brutus says Caesar was ambitious.
- He tells the crowd about something that Caesar did for Rome that shows he wasn't ambitious.
- Then he says: But Brutus says he was ambitious, and Brutus is an honorable man.
Of course, Antony means that Brutus is not an honorable man, and he is wrong to have killed Caesar because of Caesar's alleged ambition. This use of verbal irony is probably the most important reason for the speech's fame.