Chiron, called by Homer the most righteous of the Centaurs (Iliad 11.832), was the son of Kronos and the nymph Philyra. In order to elude his wife Rhea, Kronos turned them both into horses for their mating, thus producing an immortal child who was half man and half horse. Chiron was famous for his skill in music, medicine, and surgery, which he taught to heroes such as Jason, Aesclepius, and Achilles, his great-grandson.
Although Umbricius refers here to a statue of Chiron, artifacts such as the fresco above from Pompeii suggest that centaurs were a popular subject for artists.
Accidentally wounded by Herakles with a poisoned arrow in his battle with the centaurs and unable to die, Chiron suffered terrible pains from the incurable hydra poison until he was allowed finally to exchange his immortality for Prometheus' life. At his death he was taken up into the heavens as the constellation Sagittarius.