Originally, Chiron was a Thessalian god of healing, but in later Greek mythology he survived as one of the centaurs. Unlike the others of his race, Chiron was wise and had an extensive knowledge of the healing arts. He had been the tutor of, among others, Asclepius, Theseus, and Achilles. When he was accidentally hit by a poisonous arrow shot by Heracles, Chiron relinquished his immortality (in favor of Prometheus) in order to escape the pain by dying. After his death he became the constellation of Sagittarius. Chiron is regarded as a son of Cronus and Philyra.