Was there a King named

2 Kings 17:4 But the king of Assyria discovered that Hoshea was a traitor, for he had sent envoys to So king of Egypt, and he no longer paid tribute to the king of Assyria, as he had done year by year. Therefore Shalmaneser seized him and put him in prison.

The NIV text note says "Sais" is a place in Egypt. The name "So" may be a variation of Osokon IV, king of Tanis and Bubastis in the eastern delta of Egypt. Hobbs offers the following solutions:

So (to) the king of Egypt. The present syntax appears to regard the two as appositional phrases, and has resulted in a long search for the identity of So, king of Egypt. He has been identified with Pharaoh Shabaka, with the Sibe of the reports of Sargon (see ANET, 28485), and even with an unknown Arabian on the reading of Mizrayim as Musri, which is seen at times as the Akkadian designation for Arabia. In the first case the dates are wrong. Shabaka reigned from 710 to 696 B.C. In the second case, Sibe is never designated as king of Egypt. Third, the designation of the Hebrew Mizrayim as the equivalent of the Akkadian Musri is problematic. Such transferences of meaning from one language to another are very difficult to prove, and it is also doubtful whether in fact Musri denotes anything other than Egypt in Mesopotamian sources. Most now regard So as the name of a city, possibly the capital of Tefnakhte in the Delta region. Syntactically, the phrase king of Egypt is then to be read as an adverbial phrase.

Reference:

Hobbs, T. R. Vol. 13: Word Biblical Commentary, Vol. 13, 2 Kings (229). Dallas: Word, Incorporated, 2002.