Thetis (Θέτις) is of pre-Greek origin. **The chief of the fifty Nereid sea-nymphs, daughter of Nereus and Doris** — **forced to marry the mortal Peleus when an oracle predicted her son would be greater than his father** (Zeus and Poseidon had both sought her hand and withdrew). **Mother of Achilles** — she famously dipped her infant in the River Styx, gripping him by the heel, leaving only that one spot vulnerable. **The wedding of Peleus and Thetis is the framing event of the entire Trojan Cycle.**
Featured throughout Homer's *Iliad* and Statius's *Achilleid*.
Thetis reduces to one — the number of Achilles's mother.