Calchas appears in the opening scenes of the Iliad, which is believed to have been based on a war conducted by the Achaeans against the powerful city of Troy in the Late Bronze Age.

Calchas was described by the chronicler Malalas in his account of the Chronography as "short, white, all grey, including the beard, hairy, a very fine seer and omen-reader".

[6] Calchas was the son of Polymele and Thestor; grandson of the seer Idmon;[7] and brother of Leucippe, Theonoe, and Theoclymenus.

[9] In Sophocles' Ajax, Calchas delivers a prophecy to Teucer suggesting that the protagonist will die if he leaves his tent before the day is out.

Before the events of the Iliad, at the beginning of the expedition, Agamemnon had to sacrifice his daughter Iphigenia to receive favorable sailing winds.

Agamemnon exploded in anger and called the prophet a "visionary of hell" (Fitzgerald translation) and accused Calchas of rendering unfair prophecies.

Later in the story, Poseidon assumes the form of Calchas in order to rouse and empower the Greek forces while Zeus is not observing the battle.