According to ancient Greek mythology, Achilles was the greatest warrior in the Trojan War.
When Achilles was a baby, his mother took him to the mythological river Styx. Legend has it that nothing could harm the person who was dipped in the river. So, Achilles’ mother dipped him in it. The plunge rendered Achilles’ body invulnerable. However, when his mother dipped him in the river she held him by his heel, which therefore was not touched by the river’s water. Thus, his heel became his body’s only vulnerable spot. This is the source of the expression ‘Achilles heel’, which means a weakness or a vulnerable spot.