Calchas was a seer in Greek mythology, son of Thestor, able to see future events based on how the birds flew. His ability was a gift by the oracular god Apollo. On the brink of the Trojan War, Agamemnon, one of the leaders of the Achaeans, angered the goddess Artemis after killing a sacred deer. As a result, no winds blew and the Greek ships were unable to sail to Troy. Calchas realised that in order to appease the goddess, Agamemnon had to sacrifice his daughter, Iphigenia. He also foresaw that Troy would fall ten years after the war started.
During the war, it was Calchas that found out the cause of the plague that spread amongst the Greeks and threatened to decimate them. Chryses, a priest of Apollo, had asked this favour from the god, after his daughter Chryseis was abducted by the Greeks. Calchas told that the woman should be returned, causing a quarel between Agamemnon and Achilles, the theme around which the Iliad is based.
There are two myths around Calchas' death. According to the first, he died out of shame after he was beaten in a contest of soothsaying by the prophet Mopsus. The other story has it that he died of laughter, when his day of death arrived and it didn't seem to become true.