Pentheus is not a typical Greek antagonist. Sure he's the guy that stands in the way of our hero and protagonist, Dionysus, making him a shoe-in for job. In a lot of ways, though, he more closely resembles a tragic hero than Dionysus does, at least according to Aristotle. For one, Pentheus has a clear hamartia. This word is most commonly translated as "tragic flaw," but is more accurately described as an "error in judgment" or a "missing of the mark."
The King makes the error of errors by trying to defy the god Dionysus. This big old mistake results in the King being ripped limb from limb by his Bacchus-crazed mother, Agave. A Messenger reports that just before Agave had her bloody way with Pentheus, he pleaded, "Have mercy on me, Mother, and because of my mistakes don't kill your son" (225). Did you catch the key word there? Pentheus admits to making a "mistake." Yep, sounds like a hamartia to us.
As Pentheus admits to doing wrong, he's also exhibiting another tell-tale sign of a tragic hero: an anagnorisis. This is when a character has a recognition or realization of some kind. Not that it does him much good. The Messenger tells us that immediately after Agave "dragged his arm off his shoulder," while the rest of the Maenads "shredded his limbs" and threw his skin around "like a ball" (225). Looks like in the world of Euripides it doesn't much matter if somebody realizes they did wrong or not. Everybody's doomed anyway.
It's pretty easy to dislike Pentheus. The dude is kind of a stuffed shirt, and a total party pooper. When Agave and the other women of Thebes run off into the mountains to dance, drink wine, and praise Dionysus, Pentheus does everything he can to squelch the revelry. We'd also like to point out, however, that Pentheus is just doing his job. What's a King supposed do when he comes home and everybody's gone totally crazy? What kind of King would he be if he let anarchy take over his fair city? You could choose to view Pentheus as just your average ordinary King caught up in very extraordinary situation.