In Greek mythology, Kalkhas Thestórides, or Calchas ("brazen") for short, was a powerful prophet.

He told the Greeks that Achilles was necessary for victory in the Trojan War, which he predicted would take ten years. He told the Greeks that they needed to return Chryseis to her father Chryses in order to get Apollo to stop sending arrows to them. He told Agamemnon why Artemis was displeased with him and that he needed to sacrifice his daughter, Iphigeneia, to appease her. Calchas died of shame after the prophet Mopsus beat him in a contest of soothsaying.