Who was the mother of the Greek hero Achilles?

The mother of the Greek hero Achilles was Thetis.

Thetis was a Nereid, one of the sea nymphs descended from the ancient sea god Nereus and the Oceanid Doris. She married the mortal hero Peleus, king of the Myrmidons, and their son was Achilles, who became the greatest Greek warrior in the Trojan War.

Thetis’s marriage was important to the wider Trojan War mythology. The wedding, held on Mount Pelion, was attended by the gods; Eris’s exclusion from the celebration led to the golden apple and, eventually, the Judgement of Paris. Thetis also repeatedly aided Achilles during the war, including obtaining new armor for him from Hephaestus after Patroclus died.

A common mix-up concerns the story that Thetis made Achilles invulnerable by dipping him in the River Styx. That famous “Achilles’ heel” episode comes from later tradition, especially Statius, not Homer’s Iliad. In another version, she tried to remove his mortality with fire and ambrosia.