Rab-Mag
Rab-mag is the title of a Babylonian official present at the fall of Jerusalem. It attaches twice to the same figure — Nergal-sharezer — as a designation borne by one of the princes of the king of Babylon when they take possession of the city.
Among the Princes at the Middle Gate
When Jerusalem falls, the Babylonian officers enter and convene as a body in the gate: "And all the princes of the king of Babylon came in, and sat in the middle gate, [to wit,] Nergal-sharezer, Samgar-nebo, Sar-sechim the Rabsaris, Nergal-sharezer the Rabmag, with all the rest of the princes of the king of Babylon" (Jer 39:3). Rabmag here is paired with Rabsaris as titles distinguishing two of the named officers.
In the Recovery of Jeremiah
The same title reappears in the operation that retrieves Jeremiah from the court of the guard: "So Nebuzaradan the captain of the guard sent, and Nebushazban, Rab-saris, and Nergal-sharezer, Rab-mag, and all the chief officers of the king of Babylon" (Jer 39:13). Nergal-sharezer carries the Rab-mag designation again, now alongside Nebushazban as Rab-saris, in the company of "all the chief officers of the king of Babylon."