Who was (reputed to be) Alexander The Great's real father?

Question

Macedonian rumor had it that Alexander was not the son of Philip II. This rumor was based on the main ground that Philip II had several official wives a fact which infuriated Olympias, Alexander's mother. Another cause is that Philip II's many sons wanted to inherit the title of King of Macedonia. He was also rumored not to look like his father.

In a classical way forward, Alexander or his admirers later spread the rumor that indeed with such victories, his real father had to be someone with a magic or divine profile. The real father identity was then rumored to be an exiled Pharaoh of Egypt who had indeed found refuge and protection by Philip II in Macedonia. This pharaoh is represented in middle-ages paintings as a half dragon. What was his name and how did he come to be believed to have magical powers?

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Sources: Plutarch / Alexander. E.g., describing the feud at Philip's wedding:

At the wedding of Cleopatra, whom Philip fell in love with and married, she being much too young for him, her uncle Attalus in his drink desired the Macedonians would implore the gods to give them a lawful successor to the kingdom by his niece. This so irritated Alexander, that throwing one of the cups at his head, "You villain," said he, "what, am I then a bastard?"

Note: I am not considering the question of whether such a Pharaoh existed. Of interest is the story itself. Interesting enough that it inspired artists and philosophers. (Source: Peter Sloterdijk in 'Die schrecklichen Kinder der Neuzeit' — not translated in english yet.)

Answer 1

The source of this line of rumors seems to be the Alexander romance

The Romance of Alexander is any of several collections of legends concerning the mythical exploits of Alexander the Great. The earliest version is in the Greek language, dating to the 3rd century.

The Pharoah discussed as the possible deadbeat dad would be Nectanebo:

The Persians occupied Memphis and then seized the rest of Egypt, incorporating the country into the Achaemenid Empire. Nectanebo fled south and preserved his power for some time; his subsequent fate is unknown.

Of course everyone wanted to claim a piece of the credit and lay claim to the real parenthood of Alexander:

Soon after Alexander the Great's godhood was confirmed by the Libyan Sibyl of Zeus Ammon at the Siwa Oasis, a rumor was begun that Nectanebo II, following defeat in his last battle, did not travel to Nubia but instead to the court of Philip II of Macedon in the guise of an Egyptian magician.

Since the other contender was Zeus himself:

Plutarch offered a variety of interpretations of these dreams: that Olympias was pregnant before her marriage, indicated by the sealing of her womb; or that Alexander's father was Zeus.

And of course this exiled Pharaoh Nectanebo of course must have been a great magician to seduce Olympias:

while Philip was away on campaign, Nectanebo convinced Philip's wife Olympias that Amun was to come to her and that they would father a son. Nectanebo, disguising himself as Amun, slept with Olympias and from his issue came Alexander.

Of course, having controversy about your linage never hurts when you want to rule the world:

Such legends may have emerged when Alexander was king, and possibly at his own instigation, to show that he was superhuman and destined for greatness from conception.