Ixion was originally a mortal king of the Lapiths, a tribe of Thessaly. He was reportedly father to Pirithus, the most famous companion of Theseus.
Ixion reportedly angered his people through an unholy murder. He first quarreled with his father-in-law Eioneus. He then invited the old man his place in a supposed effort of reconciliation. Once Eioneus arrived, Ixion ambushed and killed him. Thus breaking both the sacred oath of kingship and that of hospitality. His people rose against him and drove him away.
Murderers were supposed to pass a purification ritual to find absolution. But in Ixion’s case nobody wanted to help him out. Nor allowed him to settle down anywhere. At last Zeus took pity on him. Zeus himself performed the purification ritual and invited Ixion to Olympus. Ixion was allowed to test the food and drink of the Gods, becoming immortal.
But Ixion was not grateful, nor satisfied. He fell in love with Hera and tried to woo her. She was not interested and notified Zeus. Wanting to test his guest, Zeus called Nephele (personification of a Cloud) and had her take Hera’s form. Ixion proceeded to seduce nephele and have sex with her, believing she was Hera. Zeus was angered at this ungrateful guest. Yet could not kill an immortal. So proved to Ixion than immortality doesn’t mean happiness.
Ixion was bound on a wheel, “on which he is whirled by winds through the air for all eternity.” Eternally damned. His son Pirithus was later also condemned to eternal imprisonment in the Underworld. Pirithus had the bright idea of entering the Underworld while alive and abduct (and rape) Persephone. Hades was not particularly fond of that idea and retaliated. Ixion and Nephele were said to be the ancestors to a new generation of Centaurs.