Dan 7:17

17 These great beasts, which are four, are four kings, who shall arise out of the earth. 

four kings – which are four kingdoms, as explained in verse 23. The first three kingdoms are represented by 3 kings: Nebuchadnezzar, Cyrus the Great and Alexander the Great. The last King is “the Ruler of this world” (John 14:30), who will eventually rule through the Beast.