Kallisto was one of the nymphs who had taken the oath of virginity and accompanied the goddess Artemis.

She was associated with Zeus and she gave birth to the hero of Arcadia, Arcas. Artemis chased her away, turned her into a bear, and her son was taken away as well. Arcas grew up and one day, as he went to the forest to hunt, he saw his mother transformed into a bear and was about to kill her. Then Zeus, in order to prevent it, transformed him into a little bear and so Arcas recognized his mother.

However Zeus feared the wrath of his wife Hera, and so he carried them both the sky and transformed them into constellations. We know them today as Ursa Major and Ursa Minor.