Who was Belshazzar?
Belshazzar was the Chaldean king under whom Babylon was taken by Darius the Mede.
The Babylonian monuments speak a number of times of a Bel -shar -uṣur who was the "firstborn son, the offspring of the heart of" Nabunaid, the last king of the Babylonian empire, that had been founded by Nabopolassar, the father of Nebuchadnezzar, at the time of the death of Ashurbanipal, king of Assyria, in 626 bc. There is no doubt that this Belshazzar is the same as the Belshazzar of Dnl. It is not necessary to suppose that Belshazzar was at any time king of the Babylonian empire in the sense that Nebuchadnezzar and Nabunaid were. It is probable, as M. Pognon argues, that a son of Nabunaid, called Nabunaid after his father, was king of Babylon, or Babylonian king, in Harran (Haran), while his father was overlord in Babylon.
This second Nabunaid is called "the son of the offspring of the heart" of Nabunaid his father. It is possible that this second Nabundid was the king who was killed by Cyrus, when he crossed the Tigris above Arbela in the 9th year of Nabunaid his father, and put to death the king of the country (see the Nabunaid-Cyrus Chronicle col. ii, 17); since according to the Eshki-Harran inscription, Nabunaid the Second died in the 9th year of Nabunaid the First. Belshazzar may have been the son of the king who is said in the same chronicle to have commanded the Babylonian army in Accad from the 6th to the 11th year of Nabunaid I; or, possibly longer, for the annals before the 6th and after the 11th year are broken and for the most part illegible.
This same son of the king is most probably mentioned again in the same chronicle as having died in the night in which Babylon was captured by Gobryas of Gutium. As Nabunaid II, though reigning at Hatran under the overlordship of his father, is called king of Babylon on the same inscription on which his father is called by the same title; so Belshazzar may have been called king of Babylon, although he was only crown prince. It is probable also, that as Nabunaid I had made one of his sons king of Harran, so he had made another king of Chaldea. This would account for Belshazzar's being called in Daniel 5:30 the Chaldean king, although, to be sure, this word Chaldean may describe his race rather than his kingdom.
The 3rd year of Belshazzar spoken of in Daniel 8:1 , would then refer to his 3rd year as subking of the Chaldeans under his father Nabunaid, king of Babylon, just as Cambyses was later subking of Babylon, while his father Cyrus was king of the lands. From the Book of Daniel we might infer that this subkingdom embraced Chaldea and Susiana, and possibly the province of Babylon; and from the Nabunaid-Cyrus Chronicle that it extended over Accad as well.
That the city of Babylon alone was sometimes at least governed by an official called king is highly probable, since the father of Nergal -shar -uṣur is certainly, and the father of Nabunaid I is probably, called king of Babylon, in both of which cases, the city, or at most the province, of Babylon must have been meant, since we know to a certainty all of the kings who had been ruling over the empire of Babylon since 626 bc, when Nabopolassar became king, and the names of neither of these fathers of kings is found among them.
In addition to Nabunaid II, Belshazzar seems to have had another brother named Nebuchadnezzar, since the two Babylonian rebels against Darius Hystaspis both assumed the name of Nebuchadnezzar the son of Nabunaid (see the Behistun Inscription, I, 85, 89, 95). He had a sister also named Ina-esagilaremat, and a second named probably Ukabu'shai' -na .
Belshazzar had his own house in Babylon, where he seems to have been engaged in the woolen or clothing trade. He owned also estates from which he made large gifts to the gods. His father joins his name with his own in some of his prayers to the gods, and apparently appointed him commander of the army of Accad, whose especial duty it was to defend the city of Babylon against the attacks of the armies of Media and Persia.
It would appear from the Nabunaid-Cyrus Chronicle, that Belshazzar was de facto king of the Babylonian empire, all that was left of it, from the 4th to the 8th month of the 17th year of the reign of his father Nabunaid, and that he died on the night in which Babylon was taken by Gobryas of Gutium (that is, probably, DARIUS THE MEDE (which see)).
The objection to the historical character of the narrative of Daniel, based upon the fact that Belshazzar in Daniel 5:11 , Daniel 5:18 is said to have been the son of Nebuchadnezzar whereas the monuments state that he was the son of Nabunaid, is fully met by supposing that one of them was his real and the other his adoptive father; or by supposing that the queen-mother and Daniel referred to the greatest of his predecessors as his father, just as Omri is called by the Assyrians the father of Jehu, and as the claimants to the Medo-Pers throne are called on the Behistun Inscription the sons of Cyaxares, and as at present the reigning sheikhs of northern Arabia are all called the sons of Rashid, although in reality they are not his sons.
IBSE (in the public domain) with minor edits.