In Greek mythology, Achilles was a Greek hero of the Trojan War and the central character and greatest warrior of Homer's Iliad. His mother was the immortal nymph Thetis, and his father, the mortal Peleus, was the king of the Myrmidons.                                                                                  

Achilles's heel

is a weakness in spite of overall strength, which can actually or potentially lead to downfall. While the mythological origin refers to a physical vulnerability, idiomatic references to other attributes or qualities that can lead to downfall are common.                                                

In Greek mythology, when Achilles was a baby, it was foretold that he would die young. To prevent his death, his mother Thetis took Achilles to the River Styx, which was supposed to offer powers of invulnerability, and dipped his body into the water; however, as Thetis held Achilles by the heel, his heel was not washed over by the water of the magical river. Achilles grew up to be a man of war who survived many great battles. One day, a poisonous arrow shot at him was lodged in his heel, killing him shortly afterwards.