In Greek mythology, the nymph Io was the daughter of the river god, Inachus. Zeus admired the beautiful Io and used often to visit her. One day when in her company he saw Hera, his jealous wife, approaching. He instantly transformed Io into a heifer. Hera was suspicious, however. She pretended to admire the heifer and finally asked Zeus to give her the beautiful creature. Zeus could not refuse. Hera gave the heifer into the charge of the hundred-eyed Argus. Zeus sent Mercury to Io's relief. Mercury succeeded in slaying Argus, but Hera now sent a gadfly to torment Io. The gadfly drove her over the whole world. She swam the Ionian Sea, which received its name from this circumstance, and finally reached the banks of the river Nile. Hera at last consented to restore Io to the form of a nymph on condition that Zeus pay her no farther attention.
