According to the Hebrew Bible, Belshazzar is the King of Babylon mentioned in the Book of Daniel, chapters 5 and 8; he is identified as the son of Nebuchadnezzar and as the last king before the advent of the Medes and Persians.

The name appears also in Baruch i. 11 as "Balthasar" (R. V. "Baltasar"). The allusions to this person in Baruch and elsewhere in extracanonical literature are all based on the data given by Dan. v. and viii.

It is stated in Dan. v. that Belshazzar gave a banquet to the lords and ladies of his court. In this court the sacred vessels of the Temple in Jerusalem, which had been brought to Babylon by Nebuchadnezzar at the time of the Judean captivity in 586 B.C., were profaned by the ribald company. In consequence of this, during the festivities, a hand was seen writing on the wall of the chamber a mysterious sentence which defied all attempts at interpretation until the Hebrew sage Daniel was called in. According to the story, Daniel read and translated the unknown words, which proved to be a divine menace against the dissolute Belshazzar, whose kingdom was to be divided between the Medes and Persians. In the last verse we are told that Belshazzar was slain in that same night, and that his power passed to Darius the Mede

This event was followed immediately afterwards by the Persian conquest of Babylon. This Biblical story is the source of the popular phrase "the writing is on the wall" as an euphemism for doom, especially impending doom that is so obvious only a fool would not see it coming.

In classical rabbinic literature

Belshazzar appears in many works of classical Jewish rabbinic literature.

The chronology of the three Babylonian kings is given in the Talmud as follows: Nebuchadnezzar reigned forty-five years, Evil-merodach twenty-three, and Belshazzar was monarch of Babylonia for two years, being killed at the beginning of the third year on the fatal night of the fall of Babylon (Meg. 11b).

The references in the Talmud and the Midrash to Belshazzar emphasize his tyrannous oppression of his Jewish subjects. Several passages in the Prophets are interpreted as though referring to him and his predecessors. In the passage, "As if a man did flee from a lion, and a bear met him" (Amos v. 19), the lion represents Nebuchadnezzar, and the bear, equally ferocious if not equally courageous, is Belshazzar.

The three Babylonian kings are often mentioned together as forming a succession of impious and tyrannous monarchs who oppressed Israel and were therefore foredoomed to disgrace and destruction. The verse in Isa. xiv. 22, "And I will rise up against them, saith the Lord of hosts, and cut off from Babylon name and remnant and son and grandchild, saith the Lord," is applied to the trio. "Name" refers to Nebuchadnezzar, "remnant" to Evil-merodach, "son" is Belshazzar, and "grandchild" Vashti (ib.). The command given to Abraham to cut in pieces three heifers as a part of the covenant established between him and his God, is thus elucidated, "And he said unto him, take unto me three heifers" (Gen. xv. 9). This symbolizes Babylonia, which gave rise to three kings, Nebuchadnezzar, Evil-merodach, and Belshazzar, whose doom is prefigured by this act of "cutting to pieces" (Midrash Genesis Rabbah xliv.).

The Midrash literature enters into the details of Belshazzar's death. It is stated that Cyrus and Darius were employed as doorkeepers of the royal palace. Belshazzar, being greatly alarmed at the mysterious handwriting on the wall, and apprehending that some one in disguise might enter the palace with murderous intent, ordered his doorkeepers to behead every one who attempted to force an entrance that night, even though such person should claim to bethe king himself. Belshazzar, overcome by sickness, left the palace unobserved during the night through a rear exit. On his return the doorkeepers refused to admit him. In vain did he plead that he was the king. They said, "Has not the king ordered us to put to death any one who attempts to enter the palace, though he claim to be the king himself?" Suiting the action to the word, Cyrus and Darius grasped a heavy ornament forming part of a candelabrum, and with it shattered the skull of their royal master (Cant. R. iii. 4).