Daughter of Lycaon, King of Arcadia. She was one of Artemis hunting attendants. As a companion of Artemis, Callisto would have taken a vow of
chastity. Zeus appeared to her in disguise, probably as Artemis, gained her confidence, then took advantage of her. As a result of this
encounter she conceived a son, Arcas.
She was turned into a large bear, either by Zeus as part of an attempt to hide his philandering, or by Hera out of jealously, or by Artemis out of anger that she broke her vow of chastity. Not content with Callistošs fate as a bear, Hera continued to work
against her to get Artemis to think she was a normal bear and slay her. Zeus came to the rescue turning her into the constellation Arctos, the Great Bear, also known as Ursa Major. At Zeus direction, Hermes saved Arcas from the womb and took him to be raised by Maia. She was joined by her son who became the nearby
constellation Arctophylax, the Little Bear, also known as Ursa Minor.
Continuing to hold a grudge Hera persuaded Tethys and Oceanus not to allow Callisto to enter their realm, the Ocean. Due to this Callisto must circle the North Star and never set over the horizon.