In The Tragedy of Julius Caesar, can Caesar be viewed as the protagonist?
Although Shakespeare's play is named after him, Julius Caesar is not the play's protagonist. He is certainly a very important character--and a real figure in history--but he is not Shakespeare's central character in the play. Although his ghost appears briefly later, Caesar's role in the play effectively ends in Act III with his assassination.
In addition, the protagonist is the character who earns sympathy and, sometimes, admiration. Caesar's murder is certainly cruel and painful, which perhaps earns him some sympathy, but he is not developed as a very sympathetic character. He is cold, arrogant and self-centered. He is very vain and easily flattered. He will not tolerate any political dissent in Rome. Also, Shakespeare implies that Caesar misuses his power in some respects.
Shakespeare most likely named his play after Julius Caesar, not because he is the protagonist, but because he and his assassination were so well known to Shakespeare's audience.