Io the daughter of Iasus, king of Argos and descendant of Inachus. Her mother was Melia or Lefkane. She was a priestess of Hera and became the lover of Zeus. Hera became aware of the illicit relationship. Then Zeus, to protect her from the wrath of his wife, transformed her into a cow.
Hera, however, forced Zeus to deny, with an oath (aphrodisiac oath), his illicit relationship and to hand over the beautiful cow, which he was forced to do. Hera entrusted the custody of the cow to the panoptes Argos, who alternately kept vigil with 500 of his 1,000 eyes.
Zeus instructed Mercury to end the situation and help his love by freeing Io. Hermes deafened all of Argos' eyes with the charm of the flute, and while he slept he beheaded him.
Io wandered as a cow in the area around Mycenae and then passed on to Euboea. Hera, however, did not give up her revenge and sent an oestrus (ox fly) to torment her. Then Io, pursued by the oestrus, began to wander all over Greece.
He crossed the coast of the Ionian Sea (because of which he got his name), reached Illyria, crossed all of Scythia, reached Prometheus who was tied to the Caucasus, crossed the coast of the Black Sea (because of which he changed its name, (which changed its name from Axenos Pontus to Euxenos), crossed the Bosporus (which because of her took its name (bous+poros), and finally reached Memphis in Egypt where she gave birth to Epaphos, her son by Zeus, who in the future would become the future leader of the tribe of the Danaans.