Answer: Ephialtes
Step-by-step explanation:
Ephialtes was a Malian Greek who according to Herodotus, betrayed the Greeks at Thermopylae to King Xerxes during his invasion of Greece. This act led to the death of the Spartan King, Leonidas when the Greek force was defeated.
The Greeks offered a reward for his death which happened around 470 BC. Ephialtes was never even rewarded by the Persians whom he betrayed his people to because they were then defeated at Salamis.