Io (EYE-oh). Priestess of Hera from Argos, who was transformed into a cow. Some say that Zeus became infatuated with Io and turned her into a heifer to hide her from his jealous wife Hera. Others say that Hera performed the transformation to protect her young priestess from Zeus. However that may be, Hera assigned the many-eyed Arcadian hero Argus to watch over Io. But Hermes, acting on Zeus's behalf, lulled Argus to sleep and decapitated him.