The centaurs were born from the sin of Ixion, the king of the Lapiths, a tribe from Thessaly in northern Greece. Ixion had murdered his father-in-law, Deioneus, by pushing him into a pit of burning coals after promising him a bride-price, and though Zeus, the king of the gods, cleansed him of this blood-guilt and welcomed him to Olympus, Ixion repaid this mercy with treachery. He lusted after Hera, the wife of Zeus, and tried to seize her. Zeus, learning of this, crafted a phantom from a cloud and gave it Hera's form. This cloud-nymph was named Nephele, and Ixion, deceived, lay with her. When he boasted that he had slept with the queen of the gods, Zeus bound him to a burning wheel and cast him into Tartarus, the pit beneath the world where the wicked suffer eternal torment. Nephele, pregnant from the union, gave birth to a son named Centaurus, a creature so deformed and savage that neither men nor gods would accept him. He fled to the mountains of Magnesia and there mated with the wild mares of the region, producing the race of centaurs: half human from their father, half horse from their mothers, creatures caught between two natures and at home in neither.

The centaurs made their home on Mount Pelion, the forested mountain that rises above the Gulf of Pagasae in eastern Thessaly. They lived in caves, hunted with clubs and rocks, and knew nothing of agriculture, metalwork, or wine until the heroes came among them. For the Greeks, they represented the barbarian other, the wildness that lurked at the edges of the polis, the city-state that defined civilization. They were male, for there were no female centaurs in the early myths, and their hunger for women was as insatiable as their hunger for meat. They were not evil in the cosmic sense, but they were governed by impulse rather than law, by appetite rather than reason. The Greeks saw in them a mirror of what men might become if they abandoned the constraints of society, the city, and the gods. They were the nightmare of the symposium, the drinking party where conversation and music were supposed to elevate the soul: give a centaur wine, and he would revert to beasthood.

The defining moment of centaur history came at the wedding of Pirithous, king of the Lapiths, to Hippodamia. Pirithous, who was the son of Ixion and thus kin to the centaurs through his grandfather's sin, invited them to the feast as a gesture of peace. The centaurs came down from Pelion, and at first they behaved with something like civility. But then wine was served, and the centaur Eurytion, drunk and inflamed, seized Hippodamia by the hair and tried to drag her away. The other centaurs, seeing this, rose as one and began grabbing the women of the wedding, the bridesmaids and the guests, intending to carry them off to the mountains. The Lapiths, led by Pirithous and his friend Theseus, the hero of Athens who had slain the Minotaur in the labyrinth of Crete, fought back with swords and spears. The battle raged through the palace, and the centaurs were defeated. Many were killed, including Eurytion, and the survivors fled south to Mount Pholoe in Arcadia or to the remote fastnesses of the Peloponnese. This battle, the Centauromachy, became one of the most popular subjects in Greek sculpture, carved into the metopes of the Parthenon in Athens and the west pediment of the Temple of Zeus at Olympia, where the god Apollo stands in the center bringing order to the chaos.

But not all centaurs were savage. Chiron, the son of the Titan Cronus and the Oceanid nymph Philyra, was an immortal of different stock. He was not born from Ixion's sin but from a god's dalliance, and he possessed wisdom, justice, and skill in every art. He dwelled in a cave on Mount Pelion, but his home was a school rather than a den. He taught the young Achilles, the greatest warrior of the Trojan War, the arts of music, medicine, hunting, and war. He taught Jason, the leader of the Argonauts who sailed to fetch the Golden Fleece. He taught Asclepius, who would become the god of medicine. He taught Heracles, the hero forced to complete twelve impossible labors, and Peleus, the father of Achilles. Chiron was the bridge between the wild and the civilized, the creature who proved that the centaur form could house a noble soul. Yet even he could not escape the violence of his kind. When Heracles visited the centaur Pholus, another civilized centaur who dwelled in Arcadia, the hero persuaded him to open a jar of wine that belonged to all the centaurs. The smell drew the wild centaurs from the hills, and a battle broke out. Heracles drove them off with his arrows, poisoned with the blood of the Hydra, but one arrow passed through a centaur and struck Chiron in the knee. Because Chiron was immortal, he could not die, but the wound caused him unending agony. In his pain, he chose to trade his immortality for the freedom of Prometheus, the Titan who had stolen fire for mankind and was chained to a rock in the Caucasus. Zeus granted the exchange, and Chiron died, released at last from pain, and was placed among the stars as the constellation Sagittarius or Centaurus.

Other centaurs appear in the margins of hero tales. Nessus, a black centaur who survived the battle at Pirithous's wedding, became a ferryman on the River Evenus. When Heracles and his wife Deianira needed to cross, Nessus offered to carry her, but halfway across he tried to rape her. Heracles heard her screams and shot Nessus with a poisoned arrow. Dying, Nessus told Deianira that his blood was a love charm, and she later soaked a shirt in it and gave it to Heracles, not knowing that the Hydra's poison would burn through his skin and drive him to suicide. Pholus, the civilized centaur who had hosted Heracles, died accidentally when he dropped one of the hero's poisoned arrows on his own foot. The centaurs who attacked Heracles were driven to the Peloponnese, where they continued to harass travelers until they were gradually hunted down or faded into the remote mountains. In later ages, the centaur became a symbol of the dual nature of humanity itself, the rational mind atop the animal body, the civilized face above the savage heart. Medieval alchemists used the centaur as an emblem of the union of opposites, and modern fantasy has made him a staple of children's literature, from C. S. Lewis's Narnia to J. K. Rowling's Forbidden Forest, where the centaurs read the stars and guard their secrets with bow and arrow. The centaur endures because he is us: half divine aspiration, half animal instinct, forever at war within a single breast.