Who was Achilles's mother?

The story behind the answer

Thetis is correct: she’s the sea nymph (a Nereid) who married the mortal hero Peleus and became the mother of Achilles. To protect him, Thetis tried to make Achilles invulnerable—most famously by dipping him in the River Styx, leaving only his heel untouched. In the Iliad, she appeals to Zeus for her son and later has Hephaestus forge Achilles’s magnificent armor.

Remember it this way: “Thetis toughens” Achilles—the mother who seeks divine help