Callisto and Arcas

In Greek mythology, Callisto was a nymph of Artemis, the goddess of forests and hills. Zeus wanted her and took on the shape of Artemis in order to lure her and rape her. When Zeus's wife Hera found out that Callisto was pregnant, it enraged her, and she turned her into a bear.

Callisto bore a son named Arcas. Years later when Arcas was hunting, he came upon a bear. Not knowing that it was his mother, he was about to kill her when Zeus took pity on her. He placed Callisto in the sky as Ursa Major (Great Bear in Latin) and Arcas nearby as Ursa Minor (Little Bear).

Callisto is also the name of one of Jupiter's moons.

References:

Wikipedia on Callisto
Ursa Major
Ursa Minor
Jupiter and Callisto engraving by Jacopo Amigoni