Dionysus, in Greek mythology, god of wine and vegetation, who showed mortals how to cultivate grapevines and make wine. A son of Zeus, Dionysus is usually characterized in one of two ways. As the god of vegetation—specifically of the fruit of the trees—he is often represented on Attic vases with a drinking horn and vine branches. He eventually became the popular Greek god of wine and cheer, and wine miracles were reputedly performed at certain of his festivals. Dionysus is also characterized as a deity whose mysteries inspired ecstatic, orgiastic worship. The maenads, or bacchantes, were a group of female devotees who left their homes to roam the wilderness in ecstatic devotion to Dionysus. They wore fawn skins and were believed to possess occult powers. Dionysus was good and gentle to those who honored him, but he brought madness and destruction upon those who spurned him or the orgiastic rituals of his cult.

According to tradition, Dionysus died each winter and was reborn in the spring. To his followers, this cyclical revival, accompanied by the seasonal renewal of the fruits of the earth, embodied the promise of the resurrection of the dead. The yearly rites in honor of the resurrection of Dionysus gradually evolved into the structured form of the Greek drama, and important festivals were held in honor of the god, during which great dramatic competitions were conducted. The most important festival, the Greater Dionysia, was held in Athens for five days each spring. It was for this celebration that the Greek dramatists Aeschylus, Sophocles, and Euripides wrote their great tragedies.

By the 5th century BC, Dionysus was also known to the Greeks as Bacchus, a name referring to the loud cries with which Dionysus was worshiped at the orgia, or Dionysiac mysteries. These frenetic celebrations, which probably originated in spring nature festivals, became occasions for licentiousness and intoxication. This was the form in which the worship of Dionysus became popular in the 2nd century BC in Roman Italy, where the Dionysiac mysteries were called the Bacchanalia. The indulgences of the Bacchanalia became increasingly extreme, and the celebrations were prohibited by the Roman Senate in 186 BC. In the 1st century AD, however, the Dionysiac mysteries were still popular, as evidenced by representations of them found on Greek sarcophagi.