Ephialtes

Ephialtes is a figure from ancient Greek history, known primarily for his betrayal during the Battle of Thermopylae in 480 BC. While Greek forces, led by King Leonidas of Sparta, held off the vastly larger Persian army, Ephialtes revealed a secret mountain pass to the Persians. This allowed them to outflank the Greek defenders, leading to their defeat. His actions have since symbolized treachery and betrayal, particularly in the context of loyalty to one’s country or friends. The term "ephialtes" has also come to be associated with a traitor or someone who undermines a cause.