St. Gregory Thaumaturgus was a third century Christian. In spite of having been converted to Christianity by the proto-heretic (and brilliant Church father) Origen, Gregory was a staunch defender of orthodox faith. In fact, he was so staunch that while he was camped out in the desert to escape the persecutions of the Emperor Decius, a vision of St. John the Apostle visited him to dictate a creed.
But that's not my favorite miracle. Neither are healing crowds of sick people, moving a mountain, drying up a swamp, nor changing the course of a river. Those are all impressive, of course, and I haven't done any of them, but none of them is my favorite.
His first miracle occurred in Alexandria, where he was a beginning preacher under Origen's tutelage. A notorious harlot approached him in a busy city square one day and demanded payment for services rendered. Greg gave her the benefit of the doubt, suggesting that she had mistaken him for someone else. She insisted that he was the John, even though (or perhaps because) he was so committed to abstinence and self-denial. So he asked that a friend pay what she asked. She took the money and immediately fell down in the street, frothing and foaming with demonic possession. Gregory then cast the demon from her, whereupon she rose, went forth, and sinned no more.