Harpagus, also known as Harpagos or Hypargus (Ancient Greek Ἅρπαγος; Akkadian: Arbaku), was a Median general from the 6th century BCE, credited by Herodotus as having put Cyrus the Great on the throne through his defection during the battle of Pasargadae.
When word reached Astyages that Cyrus was gathering his forces, he ordered Harpagus, as his primary general, to lead the army against Cyrus. After a three-day battle on the plain of Pasargadae, Harpagus took his revenge for the death of his son when he turned on the battlefield in favor of Cyrus, resulting in Astyages' defeat and the formation of the Persian Empire.
Herodotus accounts for the turn of Harpagus' support to a version of the cannibal feast of Thyestes. He reports that Astyages, after having a dream that his daughter, Mandane, would give birth to a king who would overthrow him, ordered Harpagus to expose the child at birth. Harpagus, reluctant to spill his own royal blood, gave the child (Cyrus) to a shepherd named Mitradates, who raised him as his own son.
Ten years later, when Cyrus was discovered alive, Astyages punished Harpagus for his disobedience by killing Harpagus' only son and feeding him to the courtier during a banquet. It is said that Harpagus did not react during the banquet, other than to gather the pieces of his son and remove them for burial. Astyages then asked his Magi (priests) for their advice about the fate of Cyrus. They told him that the boy, who had been discovered while playing king of the mountain with his friends, had fulfilled the prophecy of becoming a king, albeit in play, and was no longer a danger. On their advice, Astyages sent Cyrus to his parents, Cambyses I and Mandane, in Anšan (southwestern Iran near Shiraz).
Harpagus bided his time, sending gifts to Cyrus to keep contact with him, as he worked to turn the nobles of Media against Astyages. When they were ready, he sent a message to Cyrus, hidden in the belly of a hare, informing him the Medians would mutiny on the field, should he take arms against his grandfather.
Harpagus in historical texts 
"Astyages, as soon as Cyrus was born, sent for Harpagus, a man of his own house and the most faithful of the Medes...."
"When Cyrus beheld the Lydians arranging themselves in order of battle on this plain, fearful of the strength of their cavalry, he adopted a device which Harpagus, one of the Medes, suggested to him. He collected together all the camels that had come in the train of his army to carry the provisions and the baggage, and taking off their loads, he mounted riders upon them accoutred as horsemen. These he commanded to advance in front of his other troops against the Lydian horse..."
"Astyages, meanwhile, took the son of Harpagus, and slew him, after which he cut him in pieces, and roasted some portions before the fire, and boiled others..."
"When Cyrus grew to manhood, and became known as the bravest and most popular of all his compeers, Harpagus, who was bent on revenging himself upon Astyages, began to pay him court by gifts and messages..."
"Upon Mazares' death, Harpagus was sent down to the coast to succeed to his command. He also was of the race of the Medes, being the man whom the Median king, Astyages, feasted at the unholy banquet, and who lent his aid to place Cyrus upon the throne..."
"After conquering the Ionians, Harpagus proceeded to attack the Carians, the Caunians, and the Lycians. The Ionians and Aeolians were forced to serve in his army..."
"King Astyages called up his troops and marched against Cyrus, king of Anšan (southwest Iran), in order to meet him in battle. The army of Astyages revolted against him and in fetters they delivered him to Cyrus. Cyrus marched against the country Ecbatana; the royal residence he seized; silver, gold, other valuables of the country Ecbatana he took as booty and brought to Anšan."
Military career 
After the defeat of Astyages (550 BC) Harpagus started - according to Herodotus - a military career under the new ruler Cyrus II:
- Harpagus suggested using camels as the front line against the Lydian in Cyrus II's war against Croesus, thereby scattering the Lydian cavalry (the horses panicked at the smell of the dromedaries).
- Following a revolt by the Lydians and the death of Cyrus II's infantry commander, General Mazares, Cyrus II turned over the conquest of Asia Minor to Harpagus, who went on to serve as Cyrus II's most successful general.
- The Median general followed his victory at Lydia by conquering Ionia, Phoenicia, Caria, Lycia and many other regions of Asia Minor (except Miletus which had earned the favor of Cyrus II through their great sage Thales's advice to stay neutral in the Lydian war).
- Though feared in battle, Harpagus is said to have followed Cyrus's policy of tolerance and freedom of religion toward those he conquered.
- Harpagus was also known for innovations in engineering techniques, specifically, the use of earthwork ramps and mounds during sieges (a method later employed by Alexander the Great during his siege of Tyre) and for the use of mountain climbers to scale opponents' walls.
- Despite Harpagus' reputation for mercy, the residents of Xanthos in Lycia committed suicide rather than surrender to him, saying that they had never been conquered.
- The Phoenicians also did not wait for Harpagus' victory, stealing away on ships, abandoning their homeland for their colony of Carthage.