Achilles was a Greek hero in the Trojan War whose mother was the sea nymph Thetis. To make him immortal, Thetis dipped Achilles in the River Styx, but held him by the heel so his heel was not washed over and remained mortal. This allowed Achilles to be invulnerable in battle except for his heel. He fought bravely in the Trojan War until he was tricked into leaving by Prince Paris, who later fatally shot Achilles in his vulnerable heel with a poisoned arrow.