In Greek mythology, Porthaon (Greek: Πορθάων, genitive Πορθάονος), sometimes referred to as Parthaon or Portheus (seems related to the verb portheō and perthō, "destroy'), was the king of Calydon, husband of Euryte and father of Oeneus, Agrius, Alcathous, Melas, Leucopeus and Sterope, also of the Argonaut Laocoön by an unnamed female servant, or by Euryte too. He was the son of Agenor (by Epicaste) who was the son of Pleuron who was the son of Aetolus who was the son of Endymion. He was the brother of Demonice (also known as Demodice).
A different Parthaon was son of Periphetes and grandson of Nyctimus. He begot Aristus, Aristus begot Erymanthus, Erymanthus begot Arrhon, and Arrhon begot Psophis, one of the possible eponyms for the city of Psophis.