Callisto (mythology)

A follower of Artemis, she took a vow to remain a virgin. But Zeus fell in love with her and disguised himself as Apollo in order to lure her into his embrace. Hera, Zeus' wife, then turned Callisto into a bear out of revenge. Later, Callisto's son with Zeus, Arcas, nearly killed her in a hunt but Zeus placed them both in the sky as the constellations Ursa Major and Ursa Minor.

An alternate version: One of Artemis' companions, Callisto lost her virginity to Zeus, who had come disguised as Artemis. Enraged, Artemis changed her into a bear. Callisto's son, Arcas, nearly killed his mother while hunting, but Zeus or Artemis stopped him and placed them both in the sky as Ursa Major and Ursa Minor.

Another alternate version: Artemis killed Callisto in bear form, deliberately.

Hera was not please with the placement of Callisto and Arcas in the sky, so she asked her nurse, Tethys, to help. Tethys, a marine goddess, cursed the constellations to forever circle the sky and never drop below the horizon, hence explaining why they are circumpolar.