Half-divine son of Apollo by the Athenian princess Creusa; eponymous ancestor of the Ionian Greeks. Conceived by rape in the cave on the north slope of the Acropolis; exposed at birth and fostered as a temple-servant at Delphi; reunited with his mother in the recognition-drama that gives Euripides's Ion (~412 BCE) its title and structural shape. The play preserves both the divine-paternity truth (Apollo) and the social-paternity attribution (Xuthus son of Hellen) — Athena's closing intervention enjoins the social-paternity for political reasons, leaving Xuthus deceived. The Ionian tribal foundation is the political-mythological payoff: Ion organized the four traditional Ionian tribes (Geleontes, Hopletes, Argadeis, Aigicoreis), and the historical Ionian Greek world traced its tribal organization to him.