in Greek mythology, daughter of Nereus, wife of Peleus and mother of Achilles. The chief of the fifty Nereids, she dwelt in the depths of the sea with her father and sisters. When Dionysus leaped into the sea to escape from the pursuit of Lycurgus, king of the Thracian Edones, and Hephaestus was flung out of heaven by Zeus, both were kindly received by Thetis. Again, when Hera, Athena and Poseidon threatened to bind Zeus in chains, she sent the giant Aegaeon, who delivered him out of their hands. She was married against her will to Peleus (q.v.; see also Achilles). Thetis is used by Latin poets simply for the sea.