Who is…
So king of Egypt?

Hebrew: סוֹא —transliteration: Cow' —meaning: So

So is an ancient ruler who brought Egypt under his control, becoming a king of Egypt. This is probably the Egyptian king Osorkon IV (aka Usermaatre Osorkon IV, and Shilkanni). He is a son of queen consort Tadibast (aka Tadibastet).

He was bribed by King Hoshea of the northern Kingdom of Israel to help him against the Assyrian monarch Shalmaneser (8th century BC).

This was a return to the policy that had been successful during the reign of King Jeroboam I.

But the king of Assyria found conspiracy in Hoshea, who had sent messengers to So king of Egypt and had offered no tribute to the king of Assyria, as he had done year by year; therefore the king of Assyria shut him up and bound him in prison. —2 Kings 17:4