From BiblePortal Wikipedia

Watson's Biblical & Theological Dictionary [1]

otherwise Cyaxares, king of the Medes, and successor to Phraortes. He reigned forty years, and died A.M. 3409. He was father to Astyages, otherwise called Darius the Mede. He had two daughters, Mandane and Amyit: Mandane married Cambyses, the Persian, and was the mother of Cyrus; Amyit married Nebuchadnezzar, the son of Nabopolassar, and was the mother of Evil-merodach.

ASTYAGES, otherwise called Ahasuerus in the Greek,  Daniel 9:1 , or Cyaxares in Xenophon, or Apandus in Ctesias, was appointed by his father Cyaxares governor of Media, and sent with Nabopolassar, king of Babylon, against Saracus, otherwise called Chynaladanus, king of Assyria. These two princes besieged Saracus in Nineveh, took the city, and dismembered the Assyrian empire. Astyages was with Cyrus at the conquest of Babylon, and succeeded Belshazzar, king of the Chaldeans, as is expressly mentioned in  Daniel 5:30-31 , A.M. 3447. After his death Cyrus succeeded him, A.M. 3456.

Hastings' Dictionary of the Bible [2]

ASTYAGES (Bel 1) was the last king of Media. He was defeated and dethroned by Cyrus the Great in b.c. 550.

J. F. McCurdy.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [3]

( Ἀστυάγης , Diodorus Ἀσπάδας ) was the son and successor of Cyaxares (Smith's Dict. of Class. Biog. s.v.), and the last king of the Medes, B.C. 595-560 or B.C. 592-558, who was conquered by Cyrus (Bel and Dragon 1). The name is identified by Rawlinson and Niebuhr (Gesch. Assur's, p. 32) with Deioces = Ashdahak (Arm.), Ajis Dahaka (Pe's.), the biting snake, the emblem of the Median power. (See Darius The Mede). According to Herodotus, he married the daughter of Abyaltes (i. 74), ascended the throne B.C. 595, and reigned thirty-five years (i. 130), with great severity (i. 123). The same historian states that his daughter was married to Cambyses, a Persian noble, but that, in consequence of a dream, the king caused her child (Cyrus) to be exposed by a herdsman, who, on the contrary, brought him up, till, on attaining manhood, he dethroned his grandfather (i. 107). The account of Ctesias (who calls him Astygas, Ἀστυϊ v Γας ) makes him to have been only the father-in-law of Cyrus, by whom he was conquered and deposed, but treated with respect, until at length treacherously left to perish by a royal eunuch (Ctes. Ap. Phot. cod. 72, p. 36, ed. Bekker). Xenophon, like Herodotus, makes Cyrus the grandson of Astyages, but says that Astyages was succeeded by his son Cyaxares II, on whose death Cyrus succeeded to the vacant throne (Cyrop. 1, 5, 2). This account tallies better with the notices in the Book of Daniel ( Daniel 5:31;  Daniel 6:1;  Daniel 9:1) and Josephus (Ant. 10:11, 4), where "Darius (q.v.) the Mede" appears to be the same with this Cyaxares (q.v.). In that case Astyages will be identical with the "Ahasuerus" (q.v.) there named as the father of Darius. (See Cyrus).

International Standard Bible Encyclopedia [4]

as - tı̄´a - jē̄s ( Ἀστυάγης , Astuáges  ; or Astyigas (in Ktesias), or Istuvigu, son of Cyaxares. I, king of the Medes 585-550 bc, and predecessor of Cyrus (Bel and the Dragon verse 1)): His wife was the daughter of Alyattes, king of Lydia. The daughter of Astyages (Mandane) married a Persian, Cambyses, and a son was born to them who later became Cyrus the Great. Astyages had given orders to expose the babe; but Harpagus, on whom the task had been imposed, gave the child to a herdsman, with instructions to kill him. When the boy, who had been brought up as his own by the herdsman, arrived at the age of twelve, Astyages discovered that he was the son of Mandane. The king in wrath then had the son of Harpagus killed and served to his father as food. The latter concealed his feelings of hatred and resentment, and bided his time; and when the young Cyrus had grown to manhood, he stirred up the grandson in insurrection against Astyages, who was defeated and taken prisoner ( Herodotus i.127-30). When Astyages marched against the Persians, the Medes, under the command of Harpagus, deserted their king, and sided with the disappointed Persians; and Cyrus was crowned king. This account of Herodotus is confirmed by the Annalistic Tablet of Cyrus (RP, series ii, 159). The dethroned monarch was treated with kindness by his conqueror. According to Ktesias, a home was provided for him by Cyrus in Hyrcania.

Astyages was the last of the kings of the Manda (Media). An exceedingly shrewd man, Deioces by name, had founded the kingdom 150 years before (699-646). Phraortes was the second in line (646-624), and Cyaxares the third (624-584).