St. Ambrose was the bishop of Milan, a biblical critic, and the initiator of ideas that provided a model for medieval conceptions of church-state relations. He is also remembered as the teacher who converted St. Augustine of Hippo to Christianity. Along with Augustine, Gregory the Great, and Jerome, Ambrose was one of the first early Christian teachers to be declared a doctor of the church, a title given to Roman Catholic saints whose writings and teachings are of particular importance.