"Apostle of the Apostles" is the title given Mary Magdalene by St Thomas Aquinas. Her name comes from her home town of Magdala, a fishing village on the western shore of Lake Tiberias. St Luke the Evangelist tells us, in Chapter 8 of his Gospel, how Jesus went from town to town announcing the Good News of the Kingdom of God, and how the Twelve Apostles were with Him together with some women who had been healed of evil spirits or infirmities and were serving them. Among these was a certain "Mary, called the Magdalene, from whom seven demons came out."
Vatican News, July 22. ST. MARY MAGDALENE, DISCIPLE OF THE LORD. Click for more information.