'King of Kings' in the Bible

"Artaxerxes, king of kings, unto Ezra the priest and scribe in the law of the God of heaven: peace and salutation.

For thus sayeth the LORD God: Behold, I will bring hither Nebuchadnezzar, which is the king of Babylon and a king of kings, from the North upon Tyre: with horses, chariots, horsemen, and with a great multitude of people.

O king, thou art a king of kings: For the God of heaven hath given thee a kingdom, riches, strength, and majesty: