In your question about Shakespeare's Julius Caesar, I assume you're asking what evidence exists in the play that shows Brutus is the tragic figure. I'll tell you about the evidence, and let you break it up into three reasons if that's what you need.
Brutus makes the major decisions in the play that lead to: Caesar's assassination (he joins the conspirators); the mob rebelling against the conspirators and the civil war (he allows Antony to speak at the funeral); and his side losing the final battle (he moves his army from a sound defensive position to a weak offensive position). In other words, Brutus's poor decision-making drives the plot, conflict, and tragic conclusion. He is the protagonist. He also pays for his mistakes with his life, as do the other conspirators. That makes him the tragic figure.
Furthermore, Caesar not only dies in Act 3, but Caesar doesn't make decisions that lead to a tragic cleansing and conclusion. He rejects the crown, remember.
A tragic hero is a protagonist that faces adversity and makes a judgment error that tragically leads to their downfall. Throughout the play Julius Caesar, Brutus is considered a tragic hero. There are several significant aspects of Brutus's character that make him a tragic hero. First, Brutus comes from a prestigious family and is admired throughout Rome. His ancestors saved the Republic by defeating Rome's first tyrant, and he is close friends with the most powerful man in Rome, Julius Caesar. Second, he makes the terrible decision to allow Antony to live after Caesar's assassination. Brutus then decides to allow Antony to speak at Caesar's funeral, which incites the masses to riot against Brutus and his fellow conspirators. Third, Brutus makes the tragic decision to move his army to a weak offensive position, which allows Antony and Octavius's forces to win the final battle. Overall, Brutus was a gifted, respected individual, who was destined for greatness, yet made several bad decisions that led to his downfall.