Doctor means teacher. In the Catholic Church, it means a holy person, who expressed profound doctrinal insights within an extensive body of writings on the Faith. As of 2015, the title has been conferred by the Church upon 32 men and four women.
Eight men bore the title Doctor of the Church until 1568 when Pope St. Pius V added St. Thomas Aquinas to their ranks. The original eight men were all Fathers of the Church — four Western and four Eastern Church Fathers. The four Latin Doctors are St. Ambrose, St. Augustine, Pope St. Gregory the Great and St. Jerome. The four Greek Doctors are St. Athanasius, St. Basil, St. Gregory Nazianzen and St. John Chrysostom. Eight more Church Fathers from the patristic era, meaning prior to the eighth century, have since received the title of Doctor.
The only Doctor to be mentioned in the Catholic Code of Canon Law is St. Thomas Aquinas. Concerning the formation of seminarians canon 252 §3 states, "There are to be classes in dogmatic theology, always grounded in the written word of God together with sacred tradition; through these, students are to learn to penetrate more intimately the mysteries of salvation, especially with St. Thomas as a teacher."
Only men were designated Doctors until 1970 when Blessed Paul VI conferred the title on St. Catherine of Siena and St. Teresa of Avila. Pope St. John Paul II in 1997 bestowed the appellation upon St. Therese of Lisieux. Pope Benedict XVI, in turn, granted that distinction in 2012 to St. Hildegard of Bingen, bringing the number of female Doctors to four. The most recent title of Doctor was conferred on St. Gregory of Narek in 2015 by Pope Francis.
Writings of all saints are first reviewed by the Church for their orthodoxy prior to a saint's beatification. Regarding Doctors, however, the Church not only approves their theological writings but also promotes them to the faithful on account of their spiritual insights.
Get to know many early Doctors of the Church in season one of Church Militant's Premium show, Wisdom of the Fathers—St. John Chrysostom.