Io

In Greek mythology, Io (Greek: Ιω, "moon") was a mortal daughter of Inachus and Melia and a lover of Zeus. She bore Zeus two children, Epaphus and Keroessa, and became an ancestress of many great heroes of Greek myths.

Mythology
Io was a priestess of Hera in Argos, whose cult her father Inachus was supposed to have introduced to Argos. Zeus noticed Io and lusted after her. In one version of the myth, she initially rejected Zeus' advances until her father threw her out of his house on the advice of oracles. According to other sources, Zeus then turned Io into a heifer in order to hide her from his wife; other sources maintain that Hera herself transformed Io.

In the version of the story in which Zeus transformed Io, the deception failed and Hera begged Zeus to give her the heifer as a present, whic, having no reason to refuse, he did. Hera then set Argus Panoptes to watch Io and prevent Zeus from visiting her. Zeus then sent Hermes to distract and eventually slay Argus. According to Ovid, he did so by first lulling him to sleep by playing the pan-pipes and telling stories. Zeus freed Io, still in the form of a heifer.

In order to exact her revenge, Hera sent a gadfly to sting Io continuously, driving her to wander the world without rest. Io eventually crossed the path between the Propontis and the Black Sea, where she met Prometheus, who had been chained on Mount Caucasus by Zeus. Prometheus comforted Io with the information that she would be restored to human form and become the ancestress of the greatest of all heroes, Heracles. Io escaped across the Ionian Sea to Egypt, where she was restored to human form by Zeus. There, she gave birth to Zeus' son Epaphus and a daughter Keroessa. She later married the Egyptian king Telegonus.