His name derives from the Old Iranian Rishti Vaiga meaning "swinging the spear, lance-hurler
Astyages inherited a large empire, ruled in alliance with his two brothers-in-law, Croesus of Lydia and Nebuchadnezzar of Babylon, whose wife, Amytis, Astyages' sister, was the queen for whom Nebuchadnezzar was said to have built the Hanging Gardens of Babylon.
Married to Aryenis, the sister of King Croesus of Lydia, to seal the treaty between the two empires, Astyages ascended to the Median throne upon his father's death later that year. By her he had perhaps a daughter Amytis married to Cyrus the Great.
The reign of Astyages was noted for its both its stability and for the growth of the eastern prophet-based religion, Zoroastrianism throughout his empire, at the same time that Croesus was overseeing an explosion of secular thought in the west (through the philosophers he patronized, Thales, Solon, Aesop...), and Nebuchadnezzar was busily turning his city of Babylon into the greatest metropololis the world had yet seen.
After thirty-two years of relative stability, Astyages lost the support of his nobles during the war with Cyrus, resulting in the formation of the Persian empire.
In the account given by the ancient Greek historian Herodotus, Astyages is portrayed as a vain and superstious king. He relates that Astyages had a dream in which his daughter, Mandane gave birth to a son who would destroy his empire. Fearing this to be true, Astyages married her off to Cambyses I of Anšan, who had a reputation for being a "quiet and thoughtful prince" and whom Astyages believed to be no threat.
When a second dream warned Astyages of the dangers of Mandane's offspring, Astyages sent his general Harpagus to kill the child, who was none other than Cyrus himself. Harpagus, unwilling to spill royal blood, gave the infant to a shepherd, Mitridates, whose wife had given birth to a stillborn child. Cyrus was raised as Mitridates' own son, and Harpagus presented the stillborn child to Astyages as the dead Cyrus.
When Cyrus was found alive at age ten, Astyages spared the boy on the advice of his Magi, returning him to his parents in Anshan. Harpagus, however, did not escape punishment, as Astyages is said to have fed him his own son at a banquet.
Cyrus succeeded his father in 559, and in 553, on the advice of Harpagus, who was eager for revenge for being given the "abominable supper", Cyrus rebelled against Astyages. After three years of fighting, Astyages' troops mutinied during the battle of Pasargadae, and Cyrus conquered the Median's empire. Astyages was spared by Cyrus, and despite being taunted by Harpagus, Herodotus says he was treated well, and remained in Cyrus' court until his death.
Rather than giving the popular mythology that Cyrus was suckled by a bitch, Herodotus explains that the herdsman Mitridates lived with another of Astyages' slaves, namely a woman named 'Spaco', which he explains is Median for bitch.
The contemporary Chronicle of Nabonidus refers to the mutiny on the battlefield as the cause for Astyages' overthrow, but does not mention Harpagus by name. However, as Harpagus was Astyages' general at the battle of Pasargadae, as his family were granted high positions in Cyrus' empire after the war, and as Harpagus went on to become Cyrus' most successful general, it is possible he had something to do with the mutiny against Astyages. Cyrus then went on to pillage Astyages' capital of Ecbatana.
Ancient sources agree that after Astyages was taken by Cyrus he was treated with clemency, though the accounts differ. Herodotus says that Cyrus kept Astyages at his court during the remainder of his life, while according to Ctesias, he was made a governor of a region of Parthia and was later murdered by a political opponent, Oebaras. The circumstances of Astyages' death are not known.