The villain of Daniel 5 is Belshazzar, who only appears in this chapter. Who is this flash-in-the-pan character, Belshazzar? You might consider this a gimme question since the text says pretty clearly who he is: he’s Nebuchadnezzar’s son. The narrator says as much in 5:2, when he sends for the goblets that “Nebuchadnezzar his father” had brought from the Jerusalem temple years earlier (Dan 1:2). But in case you miss that reference, the queen says so twice (5:11), Belshazzar himself says it once (5:13), and Daniel says it twice (5:18, 22). Really, you’d have to be reading a different chapter to miss this fact.
But Belshazzar really wasn’t Nebuchadnezzar’s son. In fact, the two kings probably weren’t related at all (there’s an outside chance they were related by marriage). Belshazzar’s father was Nabonidus, the last king of Babylon, and Belshazzar himself wasn’t ever officially the king – he acted on behalf of his father, who spent the end of his reign on something of a medical leave. Nabonidus wasn’t related to Nebuchadnezzar either (unless he married one of his daughters), and he acquired the best seat in Babylon by stealing it from a descendant and legitimate successor of Nebuchadnezzar.
So, why does everyone in the chapter seem to think Belshazzar is Nebuchadnezzar’s son? The best answer for this is that they are probably speaking like good ancient Near Easterners, who spoke of “fathers” and “sons” a bit more loosely than we do. As the successor to the great king’s throne – whether by bow or by blood – Belshazzar was a “son” of Nebuchadnezzar.
Another example of this unconventional father-son bond between a great king and a usurping successor is found on the marvelous Black Obelisk of Shalmaneser III. Shalmaneser was the Assyrian king who, according to the carved relief, literally brought Israelite King Jehu to his knees. The Assyrian king touts his success on the obelisk: “The tribute of Jehu, son of Omri: I received from him silver, gold, a golden bowl, a golden vase with pointed bottom, golden tumblers, golden buckets, tin, a staff for a king [and] spears.” Shalmaneser calls Jehu the son of Omri, but Jehu was a divinely appointed usurper who fought his way to the Israelite throne, destroying the dynasty of Omri along the way (2 Kgs 9-10).
Another day we’ll see how the narrator of Daniel 5 exploits the metaphorical father-son relationship between Nebuchadnezzar and Belshazzar. He is far less concerned about the biological facts than how the successor to Nebuchadnezzar’s throne should have behaved.