There are three criteria for a Doctor of the
Church: eminent learning, a high degree of
sanctity, and
proclamation by the
Church (either through the Pope or a general council). They must have made a significant contribution to the
Catholic faith, although their writings are not necessarily free of all errors. Unlike
Fathers of the Church, Doctors of the Church may be from any era, and many are women. Some of the Doctors of the Church are also
Fathers of the Church. Doctors of the Church have an office and a mass conferred upon them. Since these are reserved for confessors, no martyrs were given the title of Doctor, hence the absence of
St. Ignatius,
St. Irenaeus, and
St. Cyprian.
The four Western doctors are Gregory the Great, Ambrose of Milan, Augustine of Hippo and Jerome. Originally they were three Eastern doctors: John Chrystostom, Basil the Great, and Gregory Nanzianzen. The western analogy of the Doctors with the Four Gospels led to the addition of a fourth Western Doctor, Athanasius. All of the Doctors are official saints.
A complete list of the 33 Doctors of the Church:
Hey wouldn't it be great if anyone who knows a lot about the Saints would like to contribue a writeup or two about some of the ones here who don't already have nodes? It sounds like a fun proposition to me! :-)