‘And the king of the south will be strong, and one of his princes, and he will be strong above him and have dominion. His dominion will be a great dominion.'
The king described here was Ptolemy I, one of Alexander's most powerful generals, who proclaimed himself king of Egypt in 304 BC. He was very ambitious and sought to extend his empire north into Cyprus, Asia Minor, and Greece. His dynasty ruled Egypt until around 30 BC.
The prince under the king of the south who would ‘be strong in excess of him' was Seleucus I, another of Alexander's prominent generals. He was given authority over Babylon in 321 BC. But another of Alexander's generals, Antigonus, took over Babylon, and Seleucus had to flee and seek help from Ptolemy I. With Ptolemy's sponsorship and superior power he was able to regain control of Babylon. This was the sense in which he was Ptolemy's prince, for he submitted to him in order to gain his military support against Antigonus. But Seleucus I eventually ruled from Phrygia in the west to the Indus in the east, including all of Babylonia, Media, and Syria, a territory much larger than Ptolemy's. His dynasty was seen as commencing in 312 BC. His descendants are the kings of the north. His dynasty lasted until 64 B.C.