Io, a princess and a priestess of Hera,
with whom Zeus was in love. To save the
girl from Hera's jealousy, Zeus turned her into white heifer. But Hera
didn't trust her husband and started to haunt and torment the poor Io,
who in her attempt to save herself wandered till Egypt, where she gave
birth to her son Epaphus and was later worshiped under the name of Isis.
The place where she crossed from Europe to Asia Minor is still called Bosphorus
('cow crossing').
See: Correggio Zeus
and Io.