Who is the most ambitious character in Shakespeare's Julius Caesar?

It would seem that there are only two characters in the play who could be considered "most ambitious." They are Julius Caesar and Cassius. Julius Caesar should be considered the most ambitious of the two men because he has much larger ambitions. He wants to be the sole monarch of the Roman World and has grandiose plans--and he almost makes it. Cassius is largely a reactionary. He is afraid of Caesar. He is thoroughly selfish and would like power to satisfy his greed for money. When Cassius and Brutus have their violent quarrel in Brutus's tent in Act 4, Scene 2, Brutus says:

Let me tell you, Cassius, you yourself
Are much condemned to have an itching palm,
To sell and mart your offices for gold
To undeservers.

Cassius responds with a threat of extreme violence because he is stung by the words his knows to be true.

I, an itching palm?
You know that you are Brutus that speaks this,
Or, by the gods, this speech were else your last.

Brutus himself is not especially ambitious. He likes solitude, meditation, and reading, These are not the traits of a man who is politically ambitious. Brutus has a hard time even persuading himself to participate in the plot against Caesar. Antony becomes more ambitious after the death of his good friend Julius Caesar, but Antony is always depicted as a hedonist, an athlete, a womanizer, a fun-lover, a heavy drinker. He is not a deep thinker or planner. His are not the traits of an ambitious man. Young Octavius may be extremely ambitious, but he only appears late in the play. He seems like a very young man who has not yet found himself. But in the future he will prove himself to be extremely ambitious. He will actually become a god and be the forebear of a whole line of Roman emperors, many of whom will also become gods. But he should not be considered as "most ambitious" in the play Julius Caesar because he is a young character and a minor character. We see Octavius fully developed in Shakespeare's Antony and Cleopatra. See also I, Claudius by Robert Graves.