Pothinus or Potheinos (early 1st century BC to 48 or 47 BC), a eunuch, was regent for Pharaoh Ptolemy XIII of the Ptolemaic dynasty of Ancient Egypt. He is most remembered for turning Ptolemy against his sister and co-ruler Cleopatra VII, thus starting a civil war, and for having Pompey decapitated and presenting the severed head to Julius Caesar.
When Ptolemy XII died in 51 BC his will stated that Ptolemy XIII and Cleopatra VII were to become co-rulers of Egypt, with the Roman Republic as their guardians. Ptolemy XIII was underage and Pothinus was appointed as his regent. The general Achillas and the rhetorician Theodotus of Chios were also guardians of the Egyptian king. When Ptolemy and Cleopatra were elevated to the status of senior rulers, Pothinus was maintained as the former's regent. Most Egyptologists believed that Pothinus used his influence to turn Ptolemy against Cleopatra. In the spring of 48 BC Ptolemy, under Pothinus's guidance, attempted to depose Cleopatra in order to become sole ruler, while Pothinus planned to act as the power behind the throne. They gained control of Alexandria, then the capital of Egypt, and forced Cleopatra out of the city. She soon organized her own army and a civil war began in Egypt, while Arsinoe IV also started to claim the throne for herself.
Rome was also enveloped in civil war, and after his defeat in the Battle of Pharsalus Pompey sought asylum in Egypt. Initially Pothinus pretended to have accepted his request but on September 29, 48 BC, Pothinus had the general murdered—hoping to win favor with Julius Caesar, who had defeated Pompey. When Caesar arrived he was presented with the head of Pompey, but he responded with grief and disgust and ordered that Pompey's body be located and given a proper Roman funeral. Pothinus had neglected to note that Caesar had been granting clemency to his enemies, including Cassius, Cicero, and Brutus. Cleopatra used Pothinus's mistake to gain favor with Caesar and eventually became his lover.
Caesar then arranged for the execution of Pothinus and the marriage of Cleopatra to Ptolemy. In the very last chapter of Commentarii de Bello Civili, however, it is described that Pothinus arranged for Achillas to attack Alexandria and upon sending a message not to hesitate but to fulfill the plan, the messengers were exposed, whereupon Caesar had Pothinus imprisoned and killed, probably with a knife. His death was shortly followed by the ten-month siege of Alexandria.
Unfortunately, only Roman and Greek sources have mentioned Pothinus. He is thus criticized for his murder of Pompey and his insidious behavior with regard to Caesar, while both measures are generally believed to have served to keep Egypt out of the ongoing Roman civil war. As it happened, however, Caesar came to emerge as the sole credible contender for his position of power, with Pompey dead and a Roman protectorate installed in Egypt.
Pothinus's brief role and death have been depicted more fancifully in dramatic literature.