In the Catholic calendar, today is the memorial for Peter of Ravenna, the Chrysologus, who is legendary for his sermons. I don't really have much to say about Peter Chrysologus himself, but I thought I'd say something about the title 'Doctor of the Church', which is an official honor bestowed by the Catholic Church on theologians whose teaching ('Doctor' here means 'Teacher') has been of special importance for the universal Church. In particular, the requirements are (1) sanctity of life; (2) excellence of teaching; and (3) a surviving body of writings that can be recommended to the faithful generally. It's also usually understood, although it's not required, that the saint not be a martyr. 'Martyr' is liturgically a title of higher rank than Doctor; so the title 'Doctor of the Church' is usually given only where there is teaching to be recognized that can't be placed under the title 'Martyr'. However, martyrs are sometimes more informally called doctors of the Church when they meet the other requirements -- Irenaeus being the most common example. There is also an intermediary state in which a saint is allowed the title for a particular region. The theologians who have received the title 'Doctor of the Church' thus far, arranged by the years of their death (sometimes approximate) and the year they were given the title in parentheses:
368 Hilary of Poitiers (1851)
373 Athanasius
373 Ephrem the Syrian (1920)
379 Basil of Caesarea
387 Cyril of Jerusalem (1883)
390 Gregory Nazianzen
397 Ambrose of Milan
407 John Chrysostom
420 Jerome
430 Augustine
444 Cyril of Alexandria (1883)
450 Peter Chrysologus (1729)
461 Leo the Great (1754)
604 Gregory the Great
636 Isidore of Seville (1722)
735 The Venerable Bede (1899)
749 John Damascene (1883)
1072 Peter Damian (1828)
1109 Anselm (1720)
1153 Bernard of Clairvaux (1830)
1231 Anthony of Padua (1946)
1274 Thomas Aquinas (1568)
1274 Bonaventure (1588)
1280 Albert the Great (1931)
1379 Catherine of Siena (1970)
1582 Teresa of Avila (1970)
1591 John of the Cross (1926)
1597 Peter Canisius (1925)
1619 Lawrence of Brindisi (1959)
1621 Robert Bellarmine (1931)
1622 Francis de Sales (1877)
1787 Alphonsus Liguori (1871)
1897 Therese of Lisieux (1997)
It is notable that there are two breaks in the list, in which a long period passes (323 and 203 respectively): one between the Patristic era and the Medieval, and the other between the Medieval era and the Post-Medieval era. This has a lot to do with the historical facts of the first seven Ecumenical Councils, the rise of the mendicant orders, and the Counter-Reformation. So the people that have been recognized as the great theologians of the Church tend to cluster around crises. The reason I haven't given some of the Doctors years of declaration is that these were the original ones: their status as Doctors of the Church grew up slowly as a matter of liturgy, and the title is not so much given to them as extended from them. But the title solidifies for them at some point in the twelfth or thirteenth centuries. Because of the split between East and West there are no Eastern Doctors after Damascene, making eight in total. There are three Carmelites (Teresa, John of the Cross, and Therese), two Jesuits (Canisius and Bellarmine), three Dominicans (Thomas, Albert, Catherine), three Franciscans (Anthony, Bonaventure, Lawrence), one Redemptorist (Liguori), and five Benedictines (Isidore [it is thought], Bede, Anselm, Bernard, Peter Damian).
