The Greek hero known for his invulnerability, except for his heel, is Achilles. He was a central figure in the Trojan War and is famous for his unmatched prowess in battle. Achilles' mother, Thetis, dipped him in the River Styx, making him nearly invincible. His heel, however, remained untouched, leading to the term "Achilles' heel" to symbolize a person’s singular point of vulnerability. This story illustrates the themes of fate and human mortality.