Thestius (not to be confused with Thespius) was a king of Pleuron in Aetolia, and the son of Ares and Demonice (or of Agenor and Epicaste, in which case Demonice was his sister).

By Eurythemis, Leucippe or some other woman he was the father of a number of children, including two sons Toxeus and Plexippus and daughters Althaea, Hypermnestra and Leda. His name may be a kind of masculine equivalent of Hestia (whom see), so that he is a domestic or 'hearth' god.