Chancellor
The chancellor appears in Scripture as a Persian state officer in Samaria during the early decades of Achaemenid rule, named only in connection with one episode: the official letter sent to Artaxerxes against the Jews returning to Jerusalem. The office stands beside the scribe in the provincial bureaucracy beyond the River.
Rehum the Chancellor
The book of Ezra introduces the office along with the man who held it. "Rehum the chancellor and Shimshai the scribe wrote a letter against Jerusalem to Artaxerxes the king in this sort: then [wrote] Rehum the chancellor, and Shimshai the scribe, and the rest of their fellow slaves, the Dinaites, and the Apharsathchites, the Tarpelites, the Apharsites, the Archevites, the Babylonians, the Shushanchites, the Dehaites, the Elamites" (Ezra 4:8-9). The chancellor is the senior signatory; the scribe is the second, and a long roster of subject peoples settled in Samaria signs after them. The letter that follows accuses the returnees of rebuilding Jerusalem as a step toward sedition.
The king's reply addresses the same two officers by title. "[Then] the king sent an answer to Rehum the chancellor, and to Shimshai the scribe, and to the rest of their fellow slaves who dwell in Samaria, and in the rest [of the country] beyond the River: Peace, and so forth" (Ezra 4:17). The king takes the chancellor and the scribe as the proper recipients of imperial correspondence about the province. The pair — chancellor with scribe — fixes the office on the map of the Persian administration in the satrapy beyond the River, and the rebuilding of Jerusalem is, for a time, halted by their letter.
The office appears nowhere else in Scripture. What it does is administrative: to write to and to be written by the king on behalf of the province.