In Greek mythology, Thestius was the son of either Ares and Demonice, or Agenor (son of Pleuron son of Aetolus) by Epicasta. He was the father of Iphicles with Leucippe (or, if Ares was his father, with Eurythemis). With Eurythemis, he may have also been the father of Althaea, Eurypylus, Evippus, Hypermnestra, Leda and Plexippus.