Most commentators on Shakespeare's Julius Caesar say that Brutus is the tragic figure. Caesar dies too early, and it's difficult to point out a tragic flaw in Caesar. He is accused of being ambitious by other characters, but there really isn't any evidence that he was, or at least there isn't any evidence that he possessed the kind of ambition that would make him a tyrant.
Brutus, in contrast, is too easily influenced by others and makes bad decisions. He causes the blood bath customary in a tragedy by allowing himself to be convinced that Caesar needs to be killed, by allowing Antony to speak at Caesar's funeral, by trusting Cassius to be honest, etc. Brutus is also truly noble, as befits a tragic hero. He may have been mistaken in joining the conspiracy to assassinate Caesar, but his motives were noble--he did it to save Rome.
In the play Julius Caesar, Brutus is considered the tragic hero. Before we begin to look at textual evidence that supports this statement, let's review the classical traits of a tragic hero. According to Aristotle a tragic hero
1. Struggles with fate
2. Has a tragic flaw
3. Suffers a reversal of fortune
4. Suffers from hubris (excessive pride)
5. suffers greater than what is deserved
While Shakespeare did not write a greek tragedy, he is certainly influenced by plays such as Oedipus Rex and Antigone.
Brutus is a noble character who struggles with killing Caesar because of his allegiance to Caesar. Ultimately, Brutus believes that killing Ceasar will best benefit Rome, and that is why he chooses to create his own fate. He is convinced of this when Cassius argues,
"Men at some time are masters of their fates/ The fault, dear Brutus, is not in our stars/ But in ourselves, that we are underlings"
This is evidence that Brutus struggles with his conception of fate. One can argue that Brutus' tragic flaw is not his ego (as it is with Caesar) or his jealousy (as it is with Cassius), but you need to ask yourself why Brutus ultimately decides to take down Caesar. Cassius manipulates Brutus with horrific predictions of what will happen to Rome and compares Caesar to a "colossus" that will destroy the Republic of Rome. (Remember Brutus is a descendent of the men who instituted the Republic). But Cassius also preys on Brutus' ego; he offers to be the "glass" that Brutus may truly seem himself as and how the people view Brutus. He also leaves phony letters for Brutus in his garden from the "people" of Rome. These letters sway Brutus' actions as well. In addition to Brutus' loyalty and ego, you could argue that Brutus' naive nature leads to his downfall. He trusts Cassius although he is aware of Cassius' personal vendetta against Caesar. He then does not kill Marc Antony when he has the chance because he doesn't want the conspirators actions to be viewed as too bloody or too cruel. He then allows Marc Antony to speak at Caesar's funeral and present his body to the audience. Brutus is motivated to do this because he of his hubris; he believes he controls Marc Antony's actions and the people of Rome.
While allowing Marc Antony to speak at Caesar's funeral, Brutus suffers a reversal of fortune. While initially greeted with praise and rejoice, Marc Antony is able to paint a picture of an innocent and loving Caesar who was murdered at the hands of his best friend because of ambition, glory, and ego. The crowd is incensed and wants to see Brutus dead; this results in a Civil War that does not end well for Brutus.
In the final scenes of the play, Brutus commits suicide by running on his sword. His final lines reveal regret for his actions and guilt for killing Caesar,
"Caesar, now be still. I killed not thee with half so good a will." (5.5.56-57).
We see a different and less vengeful Marc Antony speak over the body of Brutus. He states,
"This was the noblest Roman of them all. All the conspirators save only he Did that they did in envy of great Caesar. He only in a general honest thought And common good to all, made one of them. His life was gentle, and the elements So mixed in him that Nature might stand up And say to all the world, “This was a man.” (5.5.73-80).
Both of these excerpts suggest that Brutus suffered greater than he deserved. They also imply that Brutus was a good and noble character, but he was mislead by his tragic flaw. He could not be a hero if he was motivated solely by his selfishness, maliciousness, or cruelty.