In Greek mythology, Thestius was the son of either Ares and Demonice, or Agenor (son of Pleuron son of Aetolus) and Epicasta. He was the father of Iphicles with Leucippe, or Deidameia, daughter of Perieres, or else with Eurythemis, daughter of Cleoboea and mother of his other children, Althaea, Eurypylus, Evippus, Hypermnestra, Leda, Toxeus and Plexippus. In one source though, the mother of Althaea and Leda is Laophonte, daughter of Pleuron.