Cleitarchus or Clitarchus (Greek: Κλείταρχος), one of the historians of Alexander the Great, son of the historian Dinon of Colophon, was possibly a native of Egypt, or at least spent a considerable time at the court of Ptolemy Lagus.
Quintilian (Instit. x. I. 74) credits him with more ability than trustworthiness, and Cicero (Brutus, II) accuses him of giving a fictitious account of the death of Themistocles. But there is no doubt that his history was very popular, and much used by Diodorus Siculus, Quintus Curtius, Justin and Plutarch, and the authors of the Alexander romances. His unnatural and exaggerated style became proverbial.
His work, completely lost, has survived only in some thirty fragments preserved by ancient authors, especially by Aelian and Strabo.