The four kings in Daniel 11:2 are Darius Cambyses, Smerdis, Darius son of Hystapses... and then Xerxes, who was "richer than them all" and went against Greece. The "Great King" is a fifth king mentioned there, who is obviously Alexander the Great. read more
Four kings will rule Persia, one after the other, but the fourth one will become much richer than the others. In fact, his wealth will make him so powerful that he will turn everyone against the kingdom of Greece. read more