Achilles, in Greek mythology, greatest of the Greek warriors in the Trojan War. He was the son of the sea nymph Thetis and Peleus, king of the Myrmidons of Thessaly. When he was a child his mother dipped him into the River Styx to make him immortal. The waters made him invulnerable except for the heel by which his mother held him. Achilles fought many battles during the 10-year siege of Troy. When the Mycenaean king Agamemnon seized the captive maiden Briseis from him, Achilles withdrew the Myrmidons from battle and sulked in his tent. The Trojans, emboldened by his absence, attacked the Greeks and drove them into headlong retreat. Then Patroclus, Achilles' friend and companion, begged Achilles to lend him his armor and let him lead the Myrmidons into battle. Achilles consented. When Patroclus was killed by the Trojan prince Hector, the grief-stricken Achilles returned to battle, slew Hector, and dragged his body in triumph behind his chariot. He later permitted Priam, king of Troy, to ransom Hector's body. Achilles fought his last battle with Memnon, king of the Ethiopians. After killing the king, Achilles led the Greeks to the walls of Troy. There he was mortally wounded in the heel by Paris. The quarrel between Achilles and Agamemnon, the subsequent battle, and the ransoming of Hector's body are recounted in the Iliad.