Lucius Cornelius Alexander Polyhistor (Ancient Greek: Ἀλέξανδρος ὁ Πολυΐστωρ; flourished in the first half of the 1st century BC; also called Alexander of Miletus) was a Greek scholar who was enslaved by the Romans during the Mithridatic War and taken to Rome as a tutor. After his release, he continued to live in Italy as a Roman citizen. He was so productive a writer that he earned the surname polyhistor (very learned). The majority of his writings are now lost, but the fragments that remain shed valuable light on antiquarian and eastern Mediterranean subjects. Among his works were historical and geographical accounts of nearly all the countries of the ancient world, and the book Upon the Jews (Ancient Greek: Περὶ Ἰουδαίων) which excerpted many works which might otherwise be unknown.
Alexander flourished in the first half of the 1st century BC. According to the Suda he was a pupil of Crates of Mallus and a Milesian, whereas Stephanus of Byzantium claims he was a native of Cotiaeum in Lesser Phrygia and a son of Asklepiades, while the Etymologicum Magnum agrees in calling him Kotiaeus. It is possible that two different Alexandroi have been merged or confused. He became a Roman prisoner of war, was sold into slavery to a Cornelius Lentulus as his teacher (paedagogus) and was later freed. As a Roman freedman his name was Cornelius Alexander. The nomen may come from the Cornelii Lentuli or from Sulla Felix, as he received the citizenship from Sulla. He died at Laurentum in a fire which consumed his house, and his wife Helene is said by the Suda to have responded to the news of his loss by hanging herself.