Who was the traitor in the greco Persian war?

The traitor in the Greco-Persian Wars was Ephialtes of Trachis. He is infamous for betraying the Greek forces by revealing a secret mountain path to the Persian army during the Battle of Thermopylae in 480 BCE. This allowed the Persians to outflank the Greek forces, leading to their defeat. Ephialtes' act of betrayal has since become synonymous with treachery in Greek history.