In Greek mythology, Achilles ( ə-KIL-eez) or Achilleus (Greek: Ἀχιλλεύς) was a hero of the Trojan War, the greatest of all the Greek warriors, and the central character of Homer's Iliad. He was the son of the Nereid Thetis and Peleus, king of Phthia.

Achilles' most notable feat during the Trojan War was the slaying of the Trojan prince Hector outside the gates of Troy. Although the death of Achilles is not presented in the Iliad, other sources concur that he was killed near the end of the Trojan War by Paris, who shot him with an arrow. Later legends (beginning with Statius' unfinished epic Achilleid, written in the 1st century AD) state that Achilles was invulnerable in all of his body except for one heel, because when his mother Thetis dipped him in the river Styx as an infant, she held him by one of his heels. Alluding to these legends, the term "Achilles' heel" has come to mean a point of weakness, especially in someone or something with an otherwise strong constitution. The Achilles tendon is also named after him due to these legends.