CALLISTO, in Greek mythology, an Arcadian nymph, daughter of Lycaon and companion of Artemis. She was transformed into a bear as a penalty for having borne to Zeus a son, Arcas, the ancestor of the Arcadians. Hera, Zeus and Artemis are all mentioned as the authors of the transformation. Arcas, when hunting, encountered the bear Callisto, and would have shot her, had not Zeus with swift wind carried up both to the skies, where he placed them as a constellation. In another version, she was slain by Artemis. Callisto was originally only an epithet of the Arcadian Artemis herself.
See Apollodorus iii. 8; Ovid, Metam. ii. 381-530; R. Franz, De Callistus fabula (1890), which deals exhaustively with the various forms of the legend.