In Greek mythology and legendary history, Callithyia (/ˌkælɪˈθaɪ.ə/; Ancient Greek: Καλλίθυια; also Callithoe (/kəˈlɪθoʊi/; Καλλιθόη),[1] Callithea (/kəˈlɪθiə/; Καλλιθέα),[2] or Io (/ˈaɪ.oʊ/; Ἰώ Greek: [iːɔ̌ː]), "the best among women as well as among men",[3] was an Argive princess as the daughter of King Peiras[4] or Peiranthus (himself son of Argus) and the first priestess of Argive Hera in history.