What interests me most about Cleopatra's ancestry is the near certainty that she is very distantly related to Alexander the Great.

When Alexander died, there was a massive brawl between his Generals over who would rule the largest empire in human history. A very ugly brawl. Think Texas Chainsaw Massacre Meets Gladiator, only much nastier. When the dust settled, one of the few guys still standing with his intestines, limbs and head all in the expected positions was Ptolemaios.

Even in his own day the rumor was strong that Ptolemaios was the illegitimate elder half-brother of Alexander, by their father King Philip II of Macedon. Philip from a young age had been a likely lad with a propensity to bonk pretty much anything that moved, so the existence of a few extra siblings would be no surprise. Ptolemaios went a long way toward confirming this rumor by displaying during the Successor Wars the sort of strategic insight Alexander had always shown. Ptolemaios decided right away to limit himself to holding a single country, and he picked his favorite: Egypt. He kidnapped (corpse-napped?) the body of his half-brother Alexander and interred him in Alexandria, as indeed Alexander seems to have wished, and successfully held Egypt against all comers until the fighting was over.

Then he changed his name to Ptolemy and set himself up as Pharoah of Egypt. Ptolemy continued the ancient Egyptian tradition of marrying brothers to sisters to manage the succession, but he introduced a new naming scheme within the family. Almost all boys were named after him: Ptolemy. Almost all girls were named after the sister that Ptolemaios shared with Alexander the Great. Their sister, the daughter of Philip, was called...Cleopatra.

The Cleopatra was actually Cleopatra VII.