Chiron

"When first it was fashioned, the centaur lord himself affirmed its might."

- Lore

Chiron, in Greek mythology, is one of the Centaurs, the son of the Titan Cronus and Philyra, an Oceanid or sea nymph. Chiron lived at the foot of Mount Pelion in Thessaly. Unlike other Centaurs, who were violent and savage, he was famous for his wisdom and knowledge of medicine. Many Greek heroes, including Heracles, Achilles, Jason, and Asclepius, were instructed by him. Chiron frequently appears in the legends of his grandson, Peleus, and his great-grandson, Achilles. Accidentally pierced by a poisoned arrow shot by Heracles, he renounced his immortality in favor of Prometheus and was placed among the stars as the constellation Centaurus.

Hades
Though Chiron himself doesn't physically appear in the game, he is mentioned as having once wielded the Heart-Seeking Bow.

Additional notes
For additional information on Chiron that does not pertain to Hades, see Wikipedia's article: Chiron