Io was the daughter of the Greek river god Inachus. She was abducted by Zeus and disguised from Hera in the form of a cow. However, Hera saw through the ruse and kept her under watch by Argus. Zeus sent Hermes to lull Argus to sleep and steal the cow.
In some tales, Hera then sends a gadfly; Brize, and drives Io into the sea (the Ionian Sea) and she swims across the ocean to Egypt, where she is worshipped as Isis. This myth also explains to the Greeks, why Egyptians worshiped goddesses in the form of cows.
Her son with Zeus, Epaphus, would go on to rule Aethiopia and her descendants would return to Greece, ruling Mycenae, Boeotia and Argos, amongst other kingdoms. In some cases, she later married Psammetichus, king of Egypt.