Mentor of Rhodes (385-340 BC) was a Greek mercenary who fought for and against Artaxerxes III and played a part in the final major Persian military success, the reconquest of Egypt of 343 BC.
Mentor was the son of the Greek Timocrates of Rhodes. Timocrates worked for the Persians and helped trigger the Corinthian War in the 390s. This came at a time when the Spartans were campaigning in Asia Minor, and forced them to reduce their efforts in order to cope with the new crisis in Greece.
Mentor first appears during the 350s, when he supported Artabazus, satrap of Phrygia, in his revolt against Artaxerxes III of Persian (Satrap's Revolt). Mentor was supported by his younger brother Memnon, while their sister married Artabazus. The details of the revolt are somewhat unclear, but Artabazus revolted in around 358, and by 354 loyal Persian forces had reoccupied Phrygia. Memnon fled to Macedon, while Mentor escaped to Egypt, where he entered the service of Pharaoh Nectanebo II.
In 350 Mentor commanded a force of 4,000 Greek mercenaries, and repulsed an attack on Sidon in Phoenicia by a Persian satrap. However in 346/5 Artaxerxes III raised a much larger army and attacked the city for a second time. This time Mentor realised that he couldn't defend the city. Instead he betrayed it to the Persians. After his capture he was pardoned, and taken into Persian service.
In 343 Mentor took part in Artaxerxes III's successful invasion of Egypt, the last major military success for the Persian Empire. As reward he was made supreme commander of the Western Satrapies, and helped restore Persian authority in the recently rebellious areas, working closely with Bagoas, eunuch and chief minister to Artaxerxes III. Diodorus gives one example of his methods. He was given the task of defeating Hermias, tyrant of Atarneus, who had gained control over a number of other cities and fortresses. He promised Hermias that he could arrange a pardon for him, but then arrested him at a meeting. He then used Hermias's seal to send messages to his cities informing them that Mentor had arranged a reconciliation with Artaxerxes. As a result Hermias's men accepted Imperial authority without a fight.
Mentor was able to get his brother Memnon and his step-brother Artabazus pardoned, having been in exile at the court of Philip II of Macedon. Memnon entered the Persian service, and performed very well during the war against Alexander the Great.
Mentor died in 340. Memnon was appointed commander of the Troad, in the north-western corner of Asia Minor, and would go on to play a major role in the Persian resistance to Alexander the Great, before his own death in 334.