Clearchus (Ancient Greek: Kλέαρχoς, romanized: Klearkhos; c. 401 BC – 353 BC; also spelled Cleärchus or Cleärch) was a citizen of Heraclea on the Euxine (Black Sea) who was recalled from exile by the oligarchy of that city to aid them in quelling the growing discontent and demands of the people.
So he not only broke his agreement with the Mithridates, but also captured him and compelled him to pay a large sum for his release.
He was said to have used his power as badly and with as much cruelty as he had gained it and, as a sign of his arrogance, assumed publicly the attributes of Zeus, and gave the name of Keraunos (i.e. "thunderer") to one of his sons.
Thanks to his behaviour towards those he ruled over, Clearchus lived in constant fear of assassination, against which he guarded in the strictest way.
But, in spite of his precautions, he was killed by Chion and Leon in 353 BC, after a reign of twelve years.