Question: what is io the goddess of?
Answer: Io, in Greek mythology, daughter of Inachus (the river god of Argos) and the Oceanid Melia. Under the name of Callithyia, Io was regarded as the first priestess of Hera, the wife of Zeus. Zeus fell in love with her and, to protect her from the wrath of Hera, changed her into a white heifer.