He was the son of Cambyses, the prince of Persia, and was born about B.C. 599. In the year B.C. 559 he became king of Persia, the kingdom of Media being added to it partly by conquest. Cyrus was a great military leader, bent on universal conquest. Babylon fell before his army (B.C. 538) on the night of Belshazzar's feast, and then the ancient dominion of Assyria was also added to his empire.
In B.C. 536 Cyrus became king over Palestine, which became a part of his Babylonian empire. The edict of Cyrus for the rebuilding of Jerusalem marked a great epoch in the history of the Jewish people.
This decree was discovered "at Achmetha [R.V. marg., "Ecbatana"], in the palace that is in the province of the Medes" (Ezra 6:2). A chronicle drawn up just after the conquest of Babylonia by Cyrus, gives the history of the reign of Nabonidus (Nabunahid), the last king of Babylon, and of the fall of the Babylonian empire. In B.C. 538 there was a revolt in Southern Babylonia, while the army of Cyrus entered the country from the north. In June the Babylonian army was completely defeated at Opis, and immediately afterwards Sippara opened its gates to the conqueror. Gobryas (Ugbaru), the governor of Kurdistan, was then sent to Babylon, which surrendered "without fighting," and the daily services in the temples continued without a break. In October, Cyrus himself arrived, and proclaimed a general amnesty, which was communicated by Gobryas to "all the province of Babylon," of which he had been made governor. Meanwhile, Nabonidus, who had concealed himself, was captured, but treated honourably; and when his wife died, Cambyses, the son of Cyrus, conducted the funeral. Cyrus now assumed the title of "king of Babylon," claimed to be the descendant of the ancient kings, and made rich offerings to the temples. At the same time he allowed the foreign populations who had been deported to Babylonia to return to their old homes, carrying with them the images of their gods. Among these populations were the Jews, who, as they had no images, took with them the sacred vessels of the temple.
Initial text from Easton's Bible Dictionary, 1897
More text to integrate from Schaff-Herzog Encyc of Religion:
CYRUS THE GREAT (also called Cyrus the Elder, to distinguish him from Cyrus the Younger, son of Darius II., killed at Cunaxa, 401 B.C.):
Founder of the Persian Empire; b. about 600 B.C.; d. in July, 529 B.C. He belonged to the elder line of the Achaemenidae, which became extinct with the death of his son, Cambyses. Herodotus and Ctesias relate that he was of humble origin; but from inscriptions still preserved it is evident that he was of royal descent. In his cylinder inscription he designates his predecessors up to Teispes as kings of Anshan, which by some has been interpreted as Susiana, by others as the ancestral seat of the Achaemenidae.
He ascended the throne in 559, but not as an independent ruler, being forced to recognize Median overlordship. However, in 550 he conquered the last of the Median kings, Astyages, captured Ecbatana, in 546 assumed the title "king of Persia," and gained for the Persians dominion over the Iranian peoples.
An alliance was formed against Cyrus by Croesus of Lydia, Nabonidus of Babylon, and Amasis II. of Egypt; but before the allies could unite Cyrus had occupied Sardis, overthrown the Lydian kingdom, and taken Croesus prisoner (546 B.C.). In 538 there followed the occupation of Babylon by Cyrus. According to the Babylonian inscription this was in all probability a bloodless victory (see BABYLONIA, VI., 7, $ 3). From the list of countries subject to Persian rule given on the first tablet of the great Darius inscription of Behistan, written before any new conquests could have been made except that of Egypt, the dominion of Cyrus must have covered all Hither Asia and reached as far eastward as the borders of India.
According to Herodotus and Ctesias, Cyrus met his death in the year 529, while warring against tribes northeast of the headwaters of the Tigris. He was buried in the town of Pasargadae. Both Strabo and Arrian give descriptions of his tomb, based upon reports of men who saw it at the time of Alexander's invasion. The tomb northeast of Persepolis, which has been claimed as that of Cyrus, is evidently not his, as its location dose not fit the reports.
Cyrus was distinguished no less as statesman than as a soldier. His statesmanship came out particularly in his treatments of newly conquered peoples. By pursuing a policy of generosity, instead of repression, and by favoring the local religion, he was able to make his new subjects his enthusiastic supporters. A good example of this policy is found in his treatment of the Jews in Babylon.
Cyrus figures in the old Testament as the patron and deliverer of the Jews. He is mentioned twenty-three times by name and alluded to several times more, viz.: II Chron. xxxvi. 22 (twice), 3; Ezra i. 1 (twice), 2, 7, 8, iii. 7, iv. 3, 13, 14, 17, vi. 3; Isa. xliv. 28, xlv. 1; Dan. i. 21, vi. 28, x. 1. From these statements it appears that Cyrus, king of Persia, was the monarch under whom the captivity of the Jews ended, for in the first year of his reign he was prompted of Yahweh to make a decree that the temple in Jerusalem should be rebuilt and that such Jews as cared to might return to their land for this purpose. Moreover, he showed his interest in the project by sending back with them the sacred vessels which had been taken from the temple and a considerable sum of money to buy building materials with.
After the work had been stopped by enemies of the Jews it was recommended under the exhortations of the prophets, and when the authorities asked the Jews what right they had to build a temple they referred to the decree of Cyrus. Darius, who was then reigning, caused a search for this alleged decree to be made, and it was found in the Babylonian archives (Ezra vi. 2), whereupon Darius reaffirmed the decree and the work proceeded to its triumphant close. Daniel was in the favor of Cyrus, and it was in that year of Cyrus that he had the vision recorded in his tenth chapter.