Chiron was born from an act of deception. The Titan Cronus, who had castrated his father Uranus, the primordial sky-god, and seized the throne of the cosmos, was married to his sister Rhea, the goddess of fertility. But Cronus desired Philyra, one of the Oceanids, the three thousand daughters of Oceanus and Tethys, the primordial deities of the sea. To hide his infidelity from Rhea, Cronus transformed himself into a stallion and lay with Philyra in the form of a mare. When Philyra gave birth, she found herself holding a creature with the torso and head of a man and the body and legs of a horse. Horrified, she begged the gods to change her into something else, and she was transformed into a linden tree. The infant Chiron was left alone, but the gods did not abandon him. Apollo, the Olympian god of music, prophecy, and medicine who drove the sun across the sky in his golden chariot, and Artemis, his twin sister, the virgin goddess of the hunt whose silver bow never missed, took him to Mount Pelion in Thessaly, a mountain thick with forests and springs, and raised him as their own.

Under Apollo's tutelage, Chiron learned to play the lyre, to read the signs of the stars, and to heal wounds that would kill ordinary men. From Artemis he learned the art of the hunt, the tracking of beasts through the forest, and the use of the bow and spear. He grew into a creature unlike any other centaur. The other centaurs were the wild offspring of Ixion, the king of the Lapiths, who had tried to assault Hera, the queen of Olympus, and was tricked into lying with a cloud made in her shape. Those centaurs were drunken, violent, and lustful, famous for the battle at the wedding of Pirithous, the king of the Lapiths, where they tried to carry off the women and were driven out by the heroes. But Chiron was their opposite. He lived in a cave on Mount Pelion with his wife, the nymph Chariclo, and their daughter Hippe, and he welcomed mortal heroes into his home to teach them the arts of war, music, and medicine.

The list of his pupils reads like a catalogue of the greatest names in Greek myth. Peleus, the king of the Myrmidons and father of Achilles, came to Chiron as a boy, and the centaur raised him on the mountain, teaching him to wrestle and to hunt. Actaeon, the Theban hunter who would later be transformed into a stag by Artemis and torn apart by his own hounds, was another pupil. Jason, the son of Aeson, the rightful king of Iolcus who had been deposed by his half-brother Pelias, was brought to Chiron as an infant and raised in the centaur's cave until he was old enough to reclaim his throne and lead the Argonauts on their quest for the Golden Fleece. Heracles, the hero forced to complete twelve impossible labours, spent time with Chiron on Pelion, and the centaur taught him the arts of music and warfare. But the most famous of all Chiron's pupils was Achilles, the son of Peleus and the sea-goddess Thetis, who was hidden on Mount Pelion as a boy to keep him from the Trojan War. Chiron fed him the marrow of lions and bears to make him strong, taught him to play the lyre, and trained him in every art of combat until Achilles was the deadliest warrior who ever lived.

Chiron was also the teacher of Asclepius, the mortal son of Apollo and the mortal woman Coronis, who would become the god of medicine. The centaur taught him the use of herbs, the reading of dreams, and the surgery of wounds, and it was from Chiron that Asclepius learned to raise the dead, a skill so dangerous that Zeus, the king of the gods, struck him down with a thunderbolt to keep the balance between life and death. Chiron's own healing abilities were legendary. When the hero Heracles was wounded in battle, it was Chiron who treated him. But the centaur's fate was sealed by the very poison he had helped to create. Heracles had dipped his arrows in the blood of the Lernaean Hydra, the many-headed serpent whose venom was fatal to any mortal and agonising to any immortal. One day, while the centaurs were fighting with Heracles, a stray arrow from the hero's bow struck Chiron in the knee. The wound would not heal. Because Chiron was immortal, he could not die, but the Hydra's poison burned through him with unending pain.

For centuries, Chiron suffered. The gods offered him no relief, for the poison of the Hydra was beyond even their power to cure. In the end, he chose to trade his immortality for death. When Prometheus, the Titan who had stolen fire for mankind and was chained to a rock where an eagle ate his liver each day, was to be freed, Zeus demanded that an immortal must take his place in Tartarus, the dark pit beneath the earth. Chiron volunteered. He gave up his immortality and died, and in his place Prometheus was released from his torment. The gods, mourning the loss of the wisest of the centaurs, placed his image in the night sky as the constellation Centaurus, the figure of a man-horse holding a spear, forever circling the southern heavens. In some accounts, the constellation Sagittarius is also associated with him, though that figure is more often identified with Crotus, another centaur. Chiron's name survives in the word chirurgeon, the old English term for a surgeon, and in the asteroid Chiron, discovered in 1977, which orbits between Saturn and Uranus in the cold outer reaches of the solar system.