Callisto-Who

Callisto was the daughter of the Arkadian King Lykaon. She was also a hunting companion of the goddess Artemis. Callisto's name means "most beautiful." She was seduced by the god Zeus, and was later transformed into a bear. Callisto bore a son named Arkas. She was later hunted down as a beast and placed among the constellations as Ursa Major.

Picture: http://www.theoi.com/Heroine/Kallisto.html