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