The Church Fathers:

The Church Fathers were the earliest Christian theologians and writers following directly after the Apostolic Age.  The time period during which the Church Fathers were influential is referred to as the Patristic Age and expands from the 1st Century to the 8th Century.  The Church Fathers were instrumental  in determining the composition of what would become the canon of the New Testament, establishing doctrine in the early Church, maintaining unity between Churches, and distinguishing between what was traditional teaching handed down by the Apostles and what was considered erroneous, or heretical.

 The earliest Church Fathers were the Apostolic Fathers, who were believed to have personally known some of the Twelve Apostles.  They were followed by the Ante-Nicene Fathers, who were those Fathers who lived previous to the Council of Nicaea, which took place in 325 A.D.  The Nicene Era Fathers were those Fathers who lived through the Council of Nicaea or in the century directly following it.  Finally, the Post-Nicene Fathers lived sometime during the 5th through 8th Centuries.