Thetis, a sea nymph (one of the 50 Nereids), is the mother of Achilles by Peleus, king of the Myrmidons. Zeus had received a prophecy that Thetis's son would become greater than his father; therefore, in order to ensure a mortal father for her eventual offspring, Zeus and his brother Poseidon, god of the sea, made arrangements for her marriage to a man, Peleus, King of the Myrmidons.The wedding of Thetis and Peleus was celebrated on Mount Pelion and attended by all the gods. However, Eris, the goddess of Discord, had not been invited. In spite, she threw a golden apple into the midst of the goddesses that was to be awarded only to the fairest. (The award of the Golden Apple to Helen of Sparta was effected by the Judgement of Paris, Prince of Troy, and eventually caused the Trojan War).Thetis tried to make Achilles, her son by Peleus, invulnerable by dipping him in the waters of the River Styx (the river of Hades which mortals had to cross on their weay to the Underworld). However, the heel by which she held him was not protected by the Styx's waters. When Achilles is shot with an arrow by Paris in the Trojan War, the arrow hits his Achilles Tendon -- the only vulnerable spot on his body.Prophecy said that the son of Thetis would have either a long but dull life or a glorious but brief life. When the Trojan War broke out, Thetis was anxious and concealed Achilles at the court of Lycomedes, disguised as a girl. When Odysseus found that one of the girls at court was not a girl, but actually Achilles, he dressed as a merchant, and set up a table of vanity items and jewellery and called to the group. Only Achilles picked up the golden sword that lay to one side, and Odysseus quickly revealed him to be the warrior. Seeing that she could no longer prevent her son from realizing his destiny, Thetis then had Hephaestus, armorer to the gods, make a shield and armor.When Achilles was killed by Paris, Thetis came from the sea with the other Nereids to mourn him. She collected his ashes in a golden urn, raised a monument to his memory, and instituted commemorative festivals.(Source = Wikipedia) Show less «