Calchas was the son of the obscure Thestor and a great seer of Greek mythology. He accompanied the Greeks when they set out to fight the Trojan War, during which he used his prophetic skills to guide the army.
Calchas played a key role in a few episodes of the Trojan War, though his advice often caused him to clash with Agamemnon, the leader of the Greek army. It was Calchas who advised Agamemnon to sacrifice his daughter Iphigenia at Aulis and who, much later, revealed the cause of the plague ravaging the Greek camp at Troy.
Calchas died after the Trojan War when he met Mopsus, a seer who was more skilled than he.