The Early Christian Church Fathers are individuals who lived at some time after Jesus and the Apostles, but prior to about 400 AD.  They were the leaders of the Christian Faith.  Their known writings are found in a 36 volume set, the Ante-Nicene, Nicene, and Post-Nicene Fathers.  Their beliefs are in many ways different from those of main-stream Christianity today.  For example, they believed in deification, theosis or divinization, that humans can become gods, like Jesus.  They also taught on topics relevant and debated today, like abortion, which they were very much against.