The pre-Classical Greeks also believed in the ability of men to become bears. One of the most commonly told stories is that of Callisto, who bore a child of Zeus'--Arcas. Hera, Zeus' wife, became jealous and transformed Callisto into a bear as punishment. Arcas, out hunting, came upon his mother and shot at her. Zeus, taking pity on the mother and son, changed them into Ursa Major and Ursa Minor, the two great bear constellations. From this one myth comes a whole score of others.
For instance, Arcas' name comes from the Greek word for bear--Arctos. By extention, the "Arkades" of Arcadia are supposedly decended from Arcas. Their name means bear-people.
The Callisto myth also blends very well into the werewolf myth of Lycaon. According to legend, Callisto was Lycaon's daughter. Arcas was the individual who was supposed to have been served to Zeus as a test of the god's divinity, but he managed to escape. Even one of the synonyms for bear used by the Greeks, bee-wolf (for the bear's love of honey), managed to make it into legend. A legend, in fact, which was the first great work of the English language.