This question – and especially the answer to it – caused some eyebrows to be raised in the quiz that I took part in.
Alexander himself was known as Pharaoh, during his reign from 332 to 323 BC, and the rulers of the Ptolemaic dynasty (founded by one of Alexander's generals) were also known by the same title. The Ptolemaic dynasty ended in 30 BC with the Roman conquest and the death of Cleopatra.
Wikipedia clearly states that "Pharaoh ... is the common title of the monarchs of ancient Egypt from the First Dynasty (c. 3150 BCE) until the annexation of Egypt by the Roman Empire in 30 BCE."
Alexander became ruler of Egypt by dint of his conquest of the Persian Empire (which was his major achievement). The Persians had ruled Egypt since 334 BC, when Artaxerxes III overthrew the last native dynasty of Egypt (the Thirtieth).
"Artaxerxes III" is thus at least an equally acceptable answer to this question, except that he's not exactly famous (unless you happen to be an expert in this period of ancient history). But I suspect that most people, like me, would have assumed that the question referred to the fall of the Ptolemaic dynasty. If you had to pick one person as having brought this about, it would probably be Octavian (later known as Augustus Caesar) – who led the Roman forces at the Battle of Actium, the most decisive Roman victory over Antony and Cleopatra.
As I said a few questions ago, I am not a historian; I would happily stand corrected if anyone would like to put me straight.
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