The dying Achilles, Ernst Herter, from the Achilleion in Corfu
An Achilles' heel is a fatal weakness in spite of overall strength, actually or potentially leading to downfall. While the mythological origin refers to a physical vulnerability, metaphorical references to other attributes or qualities that can lead to their downfall are common.
Thetis dipping Achilles in the Styx River, Daumier 1842
The Iliad describes the death of Achilles from an heel wound from an arrow fired by Paris.
According to a myth arising later, his mother, Thetis, had dipped the infant Achilles in the river Styx, holding onto him by his heel, and he became invulnerable where the waters touched him -- that is, everywhere but the areas covered by her thumb and forefinger -- implying that only a heel wound could have been his downfall.
The use of "Achilles' heel" (or "Achilles heel") as an English expression for "area of weakness, vulnerable spot" dates only to 1855 (Merriam-Webster), or, in the form "heel of Achilles," 1810 (OED: Coleridge, "Ireland, that vulnerable heel of the British Achilles".)
Death of Achilles, Paris left shooting , in the center Apollo directs the arrows to Achilles Heel, c. 460 BC Pelike, Niobid Painter
Today the term Achilles' heel refers to any inherent weakness.
The term Achilles' tendon refers to the portion of the body below the calf and is sometimes referred to as the Achilles' heel.
Achilles (first name unknown), a baby whose mother gave him a bath, but forgot to wash all of his feet. Later was veteran of the siege of Troy. Died before receiving pension., Gordon, Irwin Leslie