Julius Caesar is a historical tragedy, usually considered one of Shakespeare's histories although distinct from his main set of biographical plays about English kings in its classical subject matter. Julius Caesar also functions less as a biography of Caesar—who dies halfway through the play—and more as an account of the political turmoil that surrounds his assassination.
As a tragedy, one might expect the tragic hero to be the eponymous character of Caesar himself. By the end of the play, however, it is Brutus—one of the conspirators who kills Caesar—who emerges as the major tragic hero, as Antony's final speech would suggest:
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.
Julius Caesar has all the requisite betrayal and death of a proper Shakespearean tragedy, particularly in the blood-soaked final act on the battlefields of Philippi. But it also functions as a carefully dramatized portrayal of the historical Roman world at the time of Caesar's assassination. Shakespeare used Greek author Plutarch's biography of Caesar as his primary source material for the historical particularities of the story, ensuring broad historical accuracy even as the bulk of the dialogue and minutiae of the play are fabricated for dramatic effect.
Even as a historical tragedy, however, Julius Caesar functions as a broad critique of the senseless violence of political power struggles. Shakespeare composed the play during a period of some uncertainty in Elizabethan England, as an aging Queen Elizabeth had yet to choose an heir and a violent struggle for the crown after her death seemed all too feasible. Shakespeare's focus on the deception and betrayal that lead to Caesar's death and the rampant bloodshed that occurs in the resultant civil war can be read as a dire warning to the English population as they face a similar predicament.