Agave was born into the most cursed royal house in Greece. Her father Cadmus had come from Phoenicia to found Thebes, slaying a great serpent that guarded a sacred spring and sowing its teeth in the earth. From those teeth sprang the Spartoi, armed men who fought one another until only five remained. One of those survivors was Echion, whom Cadmus gave to Agave as a husband. Her mother Harmonia was a goddess, the daughter of Aphrodite, goddess of love, and Ares, god of war, though some say she was the daughter of Zeus and Electra. The marriage of Cadmus and Harmonia was celebrated by all the gods on Olympus, but the serpent's curse shadowed their descendants. Agave's sisters were Semele, who was incinerated when she asked to see Zeus in his true form, Ino, who became a sea goddess after murdering her stepchildren, and Autonoe, whose son Actaeon was torn apart by his own hunting dogs when he glimpsed the goddess Artemis bathing. Agave herself married Echion and bore a son named Pentheus, a name that means "suffering," who grew up to rule Thebes after his grandfather Cadmus abdicated.

The trouble began with Dionysus, the son of Zeus and Semele, Agave's own sister. When Semele died in lightning, her sisters spread the rumour that she had lied about her divine lover and had been justly punished for her boast. They denied that Dionysus was a god at all. Years later, when Dionysus returned to Thebes as a grown man, he came in disguise as a mortal priest from Lydia, leading a band of foreign women in ecstatic worship. Pentheus, now king, refused to acknowledge the new cult. He mocked the god, imprisoned his followers, and vowed to stamp out the madness that had seized the women of his city. Dionysus did not strike him down with thunder. He struck him with something far more terrible: the god drove every woman in Thebes into a frenzy, including Agave, Autonoe, and Ino, and sent them racing up Mount Cithaeron to dance and revel in the wilderness.

Agave became one of the three leaders of the Maenads, the god-crazed women who roamed the mountain. They nursed wolf cubs and fawns at their breasts, struck rocks with their wands until wine and milk and honey flowed from the stone, and tore apart living bulls and calves with their bare hands, eating the raw flesh in a ritual called omophagia. The messenger who brought word to Pentheus described these scenes with a mixture of wonder and horror. But the worst was yet to come. Dionysus, still disguised, persuaded Pentheus to spy on the women. He dressed the king in women's clothing, arranged his curls beneath a wig, and led him to a tall pine on the mountainside. There Pentheus climbed the tree to watch the rites from above, believing he could observe without being seen. Dionysus reached up, uprooted the tree with a single gesture, and laid Pentheus gently on the ground before the Maenads.

What followed was the sparagmos, the ritual dismemberment. The women fell upon the figure before them, but the god's madness had replaced their eyes. They saw not a man in a dress but a mountain lion, a beast to be hunted and torn apart. Agave led the attack. She seized her son's right arm, planted her foot against his ribs, and tore the limb from his body with a strength no mortal woman could possess. Her sisters Autonoe and Ino joined her, and the Maenads scattered the pieces across the mountainside. Agave herself tore off Pentheus's head and impaled it upon her thyrsus, the ivy-wreathed wand of Dionysus, raising it like a hunter's trophy. She called out to the other women, boasting of the great lion she had slain, and led the procession down from Cithaeron toward the city gates.

When Agave entered Thebes, her father Cadmus was waiting. He had already gathered the fragments of Pentheus's body from the mountain, and now he watched his daughter approach with the head of her son held high. In one of the most agonising scenes in all Greek tragedy, Cadmus spoke to her gently, asking her to look at the sky, to look at what she held, to name the beast she had killed. He guided her through the fog of divine possession, question by question, until the madness lifted and Agave saw the face on her thyrsus for what it was. The recognition, the anagnorisis, shattered her. The woman who had entered the city in triumph collapsed in the dust, clutching the head of the child she had borne and nursed and destroyed. The final lines of Euripides' play, partially lost to damage in the manuscript, describe her exile from Thebes, her life unclean, her name forever joined to the worst act a mother can commit.

In a later tradition recorded by the Roman mythographer Hyginus, Agave's story did not end with exile. She travelled to Illyria, the wild land across the Adriatic, and married a king named Lycotherses. But her nature had not changed. She murdered her second husband in his bed and delivered his kingdom to her father Cadmus, who had also been exiled from Thebes and transformed into a serpent along with Harmonia. Whether this grim epilogue belongs to the older myth or is a later invention, it fits the pattern of the house of Cadmus: every generation born from the dragon's teeth seems destined to kill what it loves.