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 (a cow) in order to hide her from his wife; others maintain that Hera herself transformed Io.