The Fathers of the Church are those holy and learned teachers from the early centuries of the Catholic Church, whose writings the Church values as authoritative witnesses to Her Deposit of Faith.
The Church Fathers were either direct disciples of the Apostles or were taught by their disciples. Although not all have been declared saints, they, nonetheless, are recognized by the Church for their antiquity, orthodoxy, sanctity and ecclesiastical approval. Most lived prior to the fifth century, with one dying in the eighth century.
There are 49 Eastern or Greek Fathers and 39 Western or Latin Fathers. The last of the Western Fathers, who died in 636 A.D., was St. Isidore of Seville. The last of the Eastern Fathers, who died in 749 A.D., was St. John Damascene. The study of their writings is called patristics, from the Latin word pater meaning father.
In Magisterial documents, they're often referred to simply as the Fathers. Complete agreement by them on any point of doctrine, as evidenced by their writings, is viewed as authoritative teaching by the Magisterium. This was stated at the Council of Trent in 1546, which used the phrase "unanimous consent of the Fathers." This teaching was restated in 1870 at Vatican I which decreed, "We, renewing the same decree, declare ... that, in matters of faith and morals ... no one is permitted to interpret Sacred Scripture ... contrary to the unanimous agreement of the Fathers."
The teachings of both Trent and Vatican I, concerning the authority of the Church Fathers, were reiterated in the 1893 encyclical Providentissimus Deus by Pope Leo XIII, who wrote, "The Council of the Vatican, which, in renewing the decree of Trent declares ... that 'in things of faith and morals ... it is permitted to no one to interpret Holy Scripture ... against the unanimous agreement of the Fathers.'"
Get to know the Church Fathers starting with St. Augustine in season one of Church Militant's premium show, Wisdom of the Fathers—St. Augustine.