We're all familiar with Onkelos as a convert and a translator. According to Wikipedia,
he was a prominent Roman nobleman, the son of a man named Callinicus and the sister of Titus, the Roman emperor. According to the midrash Tanhuma, he was a nephew of Hadrian, and not Titus.
This is ahistorical, as the article continues:
Neither of these assertions are historical — Hadrian's sister, his only sibling, had a daughter, and the only child of either of Titus' siblings to survive to adulthood was also a girl, later known as Saint Flavia Domitilla.
Are there any historical references to the figure of Onkelos and his place in Roman society before his conversion?