The True Identities of Aristotle, Alexander, and Dhu’l-Qarnayn:

Our discussion here concerns the misguidance of these philosophers who build their errors upon the errors of others, relying on fabricated reports and ignorance of sound reasoning. One illustration is their claim that Aristotle was the vizier of Dhu’l-Qarnayn mentioned in the Qur’an. They heard that Aristotle had been the vizier of Alexander, and—because Dhu’l-Qarnayn is sometimes called “Alexander”—they jumped to that conclusion.

This stems from their ignorance. The Alexander whom Aristotle served was Alexander, son of Philip the Macedonian, whose story is recorded in the Roman histories known to Jews and Christians. He traveled only as far as the land of Jerusalem and, according to those familiar with his life, never reached the great barrier. He was an idol-worshipping polytheist, and so were Aristotle and his people.

Dhu’l-Qarnayn, by contrast, was a monotheist who believed in God and lived earlier than that. Those who still call him “Alexander” identify him as Alexander, son of Dara.