11. Ephialtes of Trachis
Ephialtes of Trachis is remembered as the traitor who sealed the fate of the Spartans at the Battle of Thermopylae in 480 BCE. Motivated by the promise of reward, he revealed a hidden mountain path to the invading Persian army, allowing them to outflank the Greek defenders. His act of betrayal led directly to the legendary last stand and defeat of Leonidas and his men. To this day, his name is synonymous with treachery in Greek history.
