'King of Kings' in the Bible

Artaxerxes, king of kings, unto Ezra the priest, a scribe of the law of the God of heaven, perfect peace, and at such a time.

For thus saith the Lord GOD; Behold, I will bring upon Tyrus Nebuchadrezzar king of Babylon, a king of kings, from the north, with horses, and with chariots, and with horsemen, and companies, and much people.

Thou, O king, art a king of kings: for the God of heaven hath given thee a kingdom, power, and strength, and glory.