<P> Io (/ ˈaɪ. oʊ /; Ancient Greek: Ἰώ (iːɔ̌ː)) was, in Greek mythology, one of the mortal lovers of Zeus . She was an ancestor of many kings and heroes such as Perseus, Cadmus, Heracles, Minos, Lynceus, Cepheus, and Danaus . The astronomer Simon Marius named a moon of Jupiter after Io in 1614 . </P> <P> In most versions of the legend, Io was the daughter of Inachus, though various other purported genealogies are also known . According to some sources her mother was the nymph Melia, daughter of Oceanus . The 2nd century AD geographer Pausanias also suggests that she is the daughter of Inachus and retells the story of Zeus falling in love with Io, the legendary wrath of Hera, and the metamorphosis by which Io becomes a beautiful white heifer . At another instant several generations later, Pausanias recounts another Io, descendant of Phoroneus, daughter of Iasus, who himself was the son of Argus and Ismene, the daughter of Asopus, or of Triopas and Sosis; Io's mother in the latter case was Leucane . Io's father was called Peiren in the Catalogue of Women, and by Acusilaus, possibly a son of the elder Argus, also known as Peiras, Peiranthus or Peirasus . Io may therefore be identical to Callithyia, daughter of Peiranthus, as is suggested by Hesychius of Alexandria . </P> <P> Io was a priestess of the Goddess Hera in Argos, whose cult her father Inachus was supposed to have introduced to Argos . Zeus noticed Io, a mortal woman, and lusted after her . In the version of the myth told in Prometheus Bound she initially rejected Zeus' advances, until her father threw her out of his house on the advice of oracles . According to some stories, Zeus then turned Io into a heifer in order to hide her from his wife; others maintain that Hera herself transformed Io . </P> <P> 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, which, having no reason to refuse, he did . Hera then sent Argus Panoptes, who had 100 eyes, to watch Io and prevent Zeus from visiting her, and so Zeus sent Hermes to distract and eventually slay Argus . According to Ovid, he did so by first lulling him to sleep by playing the panpipes and telling stories . Zeus freed Io, still in the form of a heifer . </P>

Why did zeus turned io into a cow