John Calvin Reformed @genevareformer

Here the angel begins to treat of the kings of Egypt and of Syria. He does not mention the king of Syria yet, but will do so in the next verse; but he begins with the king of Egypt, the neighboring monarchy to that of Israel. He says, the king of the south, meaning, the king of Egypt, would be brave. He next adds, and one of his princes.

Matthew Henry Presbyterian @wholebiblehenry

Here are foretold, I. The rise and power of two great kingdoms out of the remains of Alexander's conquests, Dan 11:5. 1. The kingdom of Egypt, which was made considerable by Ptolemaeus Lagus, one of Alexander's captains, whose successors were, from him, called the Lagidae. He is called the king of the south, that is, Egypt, named here, Dan 11:8, Dan 11:42, Dan 11:43.

Commenting on Daniel 11:5-20

John Gill Reformed Baptist @doctorgill

And the king of the south shall be strong,.... That is, the king of Egypt, which lay south to Syria, as Syria lay north to Egypt; and therefore the king of the one is called the king of the south, and the other the king of the north, throughout this prophecy; and by the king of the south, or Egypt, is here meant Ptolemy Lagus...