Rabsaris

Chief of the Heads, one of the three officers whom Sennacherib sent from Lachish with a threatening message to Jerusalem (2 Kings 18:17; Jeremiah 39:3,13).

Source: Easton's Bible Dictionary
Rabsaris

(chief of the eunuchs ). An officer of the king of Assyria sent up with Tartan and Rabshakeh against Jerusalem in the time of Hezekiah. (2 Kings 18:17) (B.C. 713.) One of the princes of Nebuchadnezzar, who was present at the capture of Jerusalem, B.C. 588. (Jeremiah 39:3,13) Rabsaris is probably rather the name of an office than of an individual.

Source: Smith's Bible Dictionary