Callisto, daughter of King Lycaon of Arcadia & companion of Artemis whose Zeus, seduced by his charms, had a son, Arcas. Hera, mad with jealousy, transformed the woman into a bear. Later, during a hunting party, Arcas finds himself in front of his mother, ready to kill her with her javelin. In order to save her, Zeus transposed it to the constellation Big Dipper. Subsequently, his son joined him in the form of the Little Dipper. Offended by the privilege granted to her rival, Hera, asking Argos, her "panoptic" shepherd, to ensure that the bears never disappear from the horizon.