Two major characters in this play who are very dissimilar are Brutus and Antony. They are both powerful leaders and generals, of high standing in Rome, but about the only other point that links these two men is that, to begin with, they are both friends of Caesar. However Brutus never appears to be an actual supporter of Caesar politically, whereas Antony is shown respectfully taking orders from him:
When Caesar says, 'Do this,' it is performed (I.ii.10)
Once Brutus is persuaded to strike against Caesar, his and Antony’s paths diverge completely, to the point that they end up leading vast armies against one another.
The most fundamental differences between these two characters are in personal temperament and political understanding. The driving force behind Brutus’s actions is his idealism. He always acts from abstract notions of honour and altruism; he is a convinced republican who sincerely believes it is better to eliminate Caesar than to give him the chance to impose one-man rule, although he does agonise over how this is to be done:
O, that we then could come by Caesar’s spirit
And not dismember Caesar! (II.i.169-170)
Brutus further believes that others share his idealism, not realising, or perhaps ignoring, the fact that the other conspirators may not be acting from the same high principles that he himself does. Even more, he misjudges the ordinary people in whose name he acts, thinking that once he explains his reasons for killing Caesar they will immediately understand and agree with him.
In a word, Brutus is naïve, to the point that he makes some fatally wrong decisions, most notably in letting Antony speak at Caesar's funeral. Antony immediately seizes his chance to win the people over to him, for, completely unlike Brutus, he is a political realist and shrewd manipulator (in this he is akin to Cassius). Their funeral speeches illustrate the differences between them. Brutus invokes abstract notions of patriotism and justice; Antony appeals directly to the crowd's personal emotions, their love for Caesar and whips up hatred for the conspirators.
Brutus generally acts and speaks with more restraint than Antony, for instance when discussing how to kill Caesar with the other conspirators, he paints an almost dignified picture of a ritual killing rather than a wanton slaying (II.i.162-180) Compare this with Antony’s blood-and-thunder speech envisaging the whole of Rome engulfed by deadly civil war in his desire for revenge upon the conspirators.
Blood and destruction shall be so in use,
And dreadful objects so familiar,
That mothers shall but smile when they behold
Their infants quartered with the hands of war,
All pity choked with custom of fell deeds (III.i.267-270)
Antony is of a notably more fiery temperament than Brutus, who himself says that
I do lack some part
Of that quick spirit that is in Antony (I.ii.28-30)
While Brutus appears as a kindly figure, not wanting to spill more blood than necessary, Antony comes across as much more ruthless in his quest for power, in Act IV scene i when in conference with Octavius and Lepidus. And Antony ultimately wins out against Brutus, although he in his turn will be deposed by his one-time ally, Octavius.