Callisto.

    Daughter of Lycaon, Callisto (also called Helice) was one of the nymphs of Artemis (Diana). She was seduced and impregnated by Zeus (Jupiter), who came to her disguised as Artemis. The maiden tried to hide her pregnancy from the goddess of chastity, but as they bathed together her transformed figure gave away her secret. In fury Artemis banished the girl, who soon gave birth to a son, Arcas.
    According to Ovid, Hera (Juno), Zeus’s jealous wife, changed Callisto into a bear. When Arcas, grown to manhood, was hunting, he tried to kill the bear, not recognizing her as his mother. In Apollodorus’s account, Zeus himself changed Callisto into a bear and she was killed unknowingly by Artemis. Ultimately, Zeus transformed Callisto into the constellation Ursa Major (the Great Bear) and Arcas into the star Arctophylax (the Bear Guardian).
    Treatments of the theme in painting most commonly depict the seduction by Zeus and the discovery of Callisto’s pregnancy in the bath. Literary and stage works often emphasize Callisto’s transformation into a bear.

Further Reference: Wall, Kathleen. 1988. The Callisto Myth from Ovid to Atwood: initiation and rape in literature. Montreal: McGill—Queen's University Press.