A lot of folks think that the myth of Dionysus, Pentheus, and Agave was made up to explain how the cult of Dionysus made its way into Greece. Some say that King Pentheus' resistance to accepting Dionysus represents how Greeks were suspicious at first of what came to them as a pretty crazy foreign religion. When the wine-god (spoiler alert!) conquers Pentheus in the end, it may represent how eventually the Greeks just couldn't help rocking out with Dionysus.
By the time this myth was finally written down, cults of Dionysus were bumpin' and grindin' all over the ancient Mediterranean. In tons of places, you could find Bacchantes out in the woods guzzling vats of wine, making bloody sacrifices, playing pipes, clashing symbols, and dancing like crazy, all just to be closer to their wild god. Well, at least we think that's what they did in their highly secretive Bacchanals (named after Bacchus, the Roman version of Dionysus). No one knows for sure exactly what went down, since these Dionysian Mysteries were only for the initiated.
All our info on the Bacchanals comes from ancient writers like Euripides, whose awesome and grisly tragedy, The Bacchae, is pretty much the definitive version of the myth. Big time Roman poet, Ovid, also puts his own spin on the story in The Metamorphoses. Other writers like Hyginius, Pseudo-Apollodorus, and Hesiod put their stamp on the myth as well, but if you ask us Euripides totally shows 'em all how it's done.