Io

Io pron.: /ˈaɪ.oʊ/ (Ancient Greek: Ἰώ [i%CB%90%C9%94%CC%8C%CB%90]%29 was, in Greek mythology, a priestess of Hera in Argos,[1] a nymph who was seduced by Zeus, who changed her into a heifer to escape detection. His wife Hera sent ever-watchful Argus Panoptes, with 100 eyes, to guard her, but Hermes was sent to distract the guardian and slay him. Heifer Io was loosed to roam the world, stung by a maddening gadfly sent by Hera, and wandered to Egypt, thus placing her descendant Belus in Egypt; his sons Cadmus and Danaus would then "return" to mainland Greece.

http://en.wikipedia.org/wiki/Io_(mythology)