Just as the title of the play suggests, Titus Andronicus is the play's "tragic hero." This is mostly because Titus is the one who suffers the most before finally getting a chance to serve up a little dish called revenge at the play's end.
At the same time, Titus's status as a protagonist or "tragic hero" doesn't necessarily mean he's an innocent victim. One could argue that Titus gets exactly what he deserves after turning Tamora's eldest son into a human sacrifice in Act 1, despite Tamora's begging and pleading. (Hmm. What does this make Tamora?) Titus is also a character who goes around killing his own children. He stabs Mutius for standing in his way in Act 1, and later he kills Lavinia so she won't have to live in "shame" after being raped. In other words, Titus is a protagonist, but he's not always the most sympathetic figure.