Euphantus in Wikipedia
Euphantus (Greek: Εὔφαντος; fl. c. 320 BCE) of Olynthus was a philosopher of the Megarian school as well as an historian and tragic poet. He was the disciple of Eubulides of Miletus, and the instructor of Antigonus I Monophthalmus king of Macedonia. He wrote many tragedies, which were well received at the games. He also wrote a very highly esteemed work, On Kingship (Greek: Περὶ Βασιλείας), addressed to Antigonus, and a history of his own times. He lived to a great age.
The Euphantus whose history is quoted by Athenaeus must be a different person, since he mentions Ptolemy III Euergetes of Egypt, as must be the Egyptian Euphantus whose translation of an Egyptian prayer is quoted by Porphyry.