(Κλέαρχος), a citizen of Heracleia on the Euxine, was recalled from exile by the nobles to aid them in quelling the seditious temper and demands of the people. According to Justin, he made an agreement with Mithridates I. of Pontus to betray the city to him on condition of holding it under him as governor. But, perceiving apparently that he might make himself master of it without the aid of Mithridates, he not only broke his agreement with the latter, but seized his person, and compelled him to pay a large sum for his release. Having deserted the oligarchical side, he came forward as the man of the people, obtained from them the command of a body of mercenaries, and, having got rid of the nobles by murder and banishment, raised himself to the tyranny. He used his power as badly, and with as much cruelty as he had gained it, while, with the very frenzy of arrogance, he assumed publicly the attributes of Zeus, and gave the name of Κεραυνός to one of his sons. He lived in constant fear of assassination, against which he guarded in the strictest way. But, in spite of his precautions, he was murdered by Chion and Leon in B. C. 353, after a reigns of twelve years. He is said to have been a pupil both of Plato and of Isocrates, the latter of whom asserts that, while he was with him, he was one of the gentlest and most benevolent of men. (Diod. 15.81, 16.36; Just. 16.4, 5; Polyaen. 2.30; Memn. apud Phot. Bibl. 224; Plut. de Alex. Fort. 2.5, ad Princ. inerud. 4; Theopomp. apud Athen. iii. p. 85; Isocr. Ep. ad Timoth. p. 423, ad fin.; Suid. s. v. Κλέαρχος; Wesseling, ad Diod. ll. cc. ; Perizon. ad Ael. V. H. 9.13.)