In Greek mythology Ino was a mortal queen of Thebes, the second wife of Athamas, the mother of Learches and Melicertes, daughter of Cadmus and Harmonia and stepmother of Phrixus and Helle. She was one of the three sisters of Semele: Agave, Autonoë and Ino, who was a surrogate for the divine nurses of Dionysus: "Ino was a primordial Dionysian woman, nurse to the god and a divine maenad" (Kerenyi 1976:246).
Maenads were known to tear their own children limb from limb in their madness. In the back-story to the heroic tale of Jason and the Golden Fleece, Phrixus and Helle, twin children of Athamas and Nephele, were hated by their stepmother, Ino. Ino hatched a devious plot to get rid of the twins, roasting all the crop seeds of Boeotia so they would not grow (Bibliotheke i.9.1). The local farmers, frightened of famine, asked a nearby oracle for assistance. Ino bribed the men sent to the oracle to lie and tell the others that the oracle required the sacrifice of Phrixus. Athamas reluctantly agreed. Before he was killed though, Phrixus and Helle were rescued by a flying golden ram sent by Nephele, their natural mother. Helle fell off the ram into the Hellespont (which was named after her, meaning Sea of Helle) and drowned, but Phrixus survived all the way to Colchis, where King Aeetes took him in and treated him kindly, giving Phrixus his daughter, Chalciope, in marriage. In gratitude, Phrixus gave the king the golden fleece of the ram, which Aeetes hung in a tree in his kingdom.
Later, Ino raised Dionysus, her nephew, son of her sister Semele, causing Hera's intense jealousy. In vengeance, Hera struck Athamas with insanity. Athamas went mad, slew one of his sons, Learchus, thinking he was a ram, and set out in frenzied pursuit of Ino. To escape him Ino threw herself into the sea with her son Melicertes. Both were afterwards worshipped as marine divinities, Ino as Leucothea ("the white goddess"), Melicertes as Palaemon. Alternatively, Ino was also stricken with insanity and killed Melicertes by boiling him in a cauldron, then took the cauldron and jumped into the sea with it. A sympathetic Zeus didn't want Ino to die, and transfigured her and Melicertes as Leucothea and Palaemon.
The story of Ino, Athamas and Melicertes is relevant also in the context of two larger themes. Ino, daughter of Cadmus and Harmonia, had an end just as tragic as her siblings: Semele died while pregnant with Zeus' child, killed by her own pride and lack of trust in her lover; Agave killed her own son, King Pentheus while struck with Dionysian madness, and Actaeon, son of Autonoe, the third sibling, was torn apart by his own hunting dogs. Also, the insanity of Ino and Athamas, who hunted his own son Learchos as a stag and slew him, can be explained as a result of their contact with Dionysus, whose presence can cause insanity. None can escape the powers of Dionysus, the god of wine. Euripides took up the tale in The Bacchae, explaining their madness in Dionysiac terms, as having initially resisted belief in the god's divinity.
When Athamas returned to his second wife, Ino, Themisto (his third wife) sought revenge by dressing her children in white clothing and Ino's in black and directing the murder of the children in black. Ino switched their clothes without Themisto knowing and she killed her own children.
Transformed into an immortal goddess, Ino also represents one of the many sources of divine aid to Odysseus in Homer's epic poem, The Odyssey. Providing him with a veil, she instructs him how he can succeed in his plight to reach land and eventually Ithaca. Homer's epithet associated with this goddess is "Ino of the slim ankles".
In historical times, a sisterhood of maenads of Thebes in the service of Dionysus traced their descent in the female line from Ino; we know this because an inscription at Magnesia on the Maeander summoned three maenads from Thebes, from the house of Ino, to direct the new mysteries of Dionysus at Magnesia (Burkert 1992:44).