Charles Ellicott Commentary 2 Kings 18:19

"And Rabshakeh said unto them, Say ye now to Hezekiah, Thus saith the great king, the king of Assyria, What confidence is this wherein thou trustest?" — 2 Kings 18:19 (ASV)

And Rab-shakeh said. —Tiglath Pileser records that he sent a rab-sak as his envoy to Tyre. Thenius supposes the present rab-sak may have been a better master of Hebrew than his companions. Schrader says it would have been beneath the tartan’s dignity to speak, and that such vigorous language as follows would have had a very strange effect in the mouth of a eunuch (the rabsaris).

The great king, the king of Assyria. —Compare the usual grandiloquent style of the Assyrian sovereigns: “I, Esarhaddon, the great king, the mighty king, the king of multitudes, the king of the country of Asshur;” and the title, king of princes, which Hosea applies to the king of Assyria (Hosea 8:10).