Harpalus (Greek: Ἅρπαλος) son of Machatas was an aristocrat of Macedon and boyhood friend of Alexander the Great in the 4th century BC. Being lame in a leg, and therefore exempt from military service, Harpalus did not follow Alexander in his advance within the Persian Empire but received nonetheless a post in Asia Minor. Alexander reportedly contacted him with a demand of reading material for his spare time. Harpalus sent his King theatrical plays by Aeschylus, Sophocles and Euripides, the history of Philistus and odes by Philoxenus and Telestes.
Harpalus was also a charming rogue who absconded three times with large amounts of money. The first time he was forgiven and reinstated, only to abuse his trust again. In 324 BC Harpalus found refuge in Athens. He was imprisoned by the Athenians after a proposal of Demosthenes and Phocion, despite Hypereides' opposition, who wanted an immediate uprising against Alexander. The Ecclesia, based on a proposal from Demosthenes, decided on the guarding of Harpalus' money, which was entrusted to a committee led by Demosthenes himself. When the committee counted the money they found 350 talents, although Harpalus had declared that he had 700 talents. Nevertheless, Demosthenes and the other members of the committee decided not to disclose the deficit.
Harpalus in Greek mythology was son of Amyclas king of Laconia and father of Deritus, ancestor of Patreus, founder of Patras.
Harpalus was an ancient Greek astronomer (flor. 82nd Olympiad, ca.450 BC) who corrected the cycle of Cleostratus and invented the Nine Year Cycle. He may also have been the engineer Harpalus who designed a pontoon bridge solution when Xerxes wished his army to cross the Hellespont.