Father: With the death of the apostle John (c. 100 AD), one of the Twelve to whom Christ gave the mission to witness to His life, death and resurrection, ended the era of Public Revelation. That Revelation is contained in the Old Testament and the apostolic writings of the New Testament, as well as in the orally communicated teaching and preaching of the apostles called Sacred Tradition (2 Thes. 2:2).

To qualify as Sacred Tradition, as opposed to human tradition representing the opinions of men, teaching must be universally taught, explicitly or implicitly, by the early Church. This is known by the extent to which a particular teaching can be found in the Church Fathers, the holy and learned men who came after the apostles, and who in most cases succeeded them as the bishops of the Church. A teaching found unanimously among the Fathers who write on it is certainly from the apostles and therefore revealed by God.

The era of the Fathers of the Church is generally considered to begin with the apostolic Fathers,  who were taught directly by the Apostles, and to end around 600 AD in the Latin speaking Church and 800 AD in the Greek.

Doctor: Over the centuries the Church's highest teaching authority, the Pope, has held up holy men and women whose teaching has been of exceptional value to the Church and who are trust worthy witnesses to the doctrine of the faith by declaring them Doctors of the Church. The most recent Doctor of the Church is St. Therese of Lisieux, declared by Pope John Paul II in 1997. 

ST. ALBERT THE GREAT (1200-80?). Dominican. Patron of natural scientists; called doctor universalis, doctor expertus.

ST. ALPHONSUS LIGUORI (1696-1787). Patron of confessors and moralists. Founder of the Redemptorists.

ST. AMBROSE (340-97). One of the four traditional Doctors of the Latin Church. Opponent of Arianism in the West. Bishop of Milan.

ST. ANSELM (1033-1109). Archbishop of Canterbury. Father of Scholasticism.

ST. ANTHONY OF PADUA (1195-1231). Franciscan Friar Evangelical Doctor.

ST. ATHANASIUS (297-373). Bishop of Alexandria. Dominant opponent of Arianism. Father of Orthodoxy.

ST. AUGUSTINE (354-430). Bishop of Hippo. One of the four traditional Doctors of the Latin Church. Doctor of Grace.

ST. BASIL THE GREAT (329-79). One of the Three Cappadocian Fathers. Father of monasticism in the East.

ST. BEDE THE VENERABLE (673-735). Benedictine priest Father of English history. 

ST. BERNARD OF CLAIRVAUX (1090-1153). Cistercian. Called Mellifluous Doctor because of his eloquence.

ST. BONAVENTURE (1217-74). Franciscan theologian. Seraphic Doctor.

ST. CATHERINE OF SIENA (1347-80). Mystic. Second. woman Doctor.

ST. CYRIL OF ALEXANDRIA (376-444). Patriarch. Opponent of Nestorianism. Made key contributions to Christololgy.

ST. CYRIL OF JERUSALEM (315-87). Bishop and opponent of Arianism in the East.

ST. EPHRAEM THE SYRIAN (306-73). Biblical exegete and ecclesiastical writer. Called Harp of the Holy Spirit.

ST. FRANCIS DE SALES (1567-1622). Bishop, leader in
Counter-Reformation. Patron of Catholic writers and the Catholic press.

ST. GREGORY I THE GREAT (540-604). Pope. Fourth and last of the traditional Doctors of the Latin Church. Defended papal supremacy and worked for clerical and monastic reform.

ST. GREGORY OF NAZIANZUS (330-90). Called the Christian Demosthenes because of his eloquence and, in the Eastern Church, The Theologian. One of the Three Cappadocian Fathers.

ST. HILARY OF POITIERS (315-68). Bishop. Called The Athanasius of the West.

ST. ISIDORE OF SEVILLE (S60-636). Archbishop, theologian, historian. Regarded as the most learned man of his time.

ST. JEROME (343-420). One of the four traditional Doctors of the Latin Church. Father of biblical science.

ST. JOHN CHRYSOSTOM (347-407). Bishop of Constantinople. Patron of preachers and called Golden- Mouthed because of his eloquence.

ST. JOHN DAMASCENE (675-749). Greek theologian. Called Golden Speaker because of his eloquence.

ST. JOHN OF THE CROSS (1542-91). Joint founder of the Discalced Carmelites. Doctor of Mystical Theology.

ST. LAWRENCE OF BRINDISI (1559-1619). Vigorous preacher of strong influence in the post-Reformation period.

ST. LEO I THE GREAT (400-61). Pope. Wrote against Nestorian and Monophysite heresies and errors of Manichaeism and Pelagianism.

ST. PETER CANISIUS (1521-97). Jesuit theologian. Leader in the Counter-Reformation.

ST. PETER CHRYSOLOGUS (400-50). Bishop of Ravenna. Called Golden-Worded.

ST. PETER DAMIAN (1007-72). Benedictine. Ecclesiastical and clerical reformer.

ST. ROBERT BELLARMINE (1542-1621). Jesuit. Defended doctrine under attack during and after the Reformation. Wrote two catechisms.

ST. TERESA OF AVILA (1515-82). Spanish Carmelite nun and mystic. First woman Doctor.

ST. THERESE OF LISIEUX (1873-1897). French Carmelite nun. Known as The Little Flower, her autobiographical "Story of a Soul" has become a spiritual classic, inspiring millions to follow her "Little Way" of holiness. Already Patroness of the Missions, she was proclaimed the third woman Doctor of the Church by Pope John Paul II on October 19th, 1997.

ST. THOMAS AQUINAS (1225-74). Dominican philosopher and theologian. Called Angelic Doctor. Patron of Catholic schools and education.