The Catechism in Questions & Answers

590. Who handed the teachings of the early Apostles down to posterity?

The original teaching of the Apostles was handed down and further developed by the “Apostolic Fathers”. These were church teachers of great influence. Their ranks included the likes of Clement of Rome (died around AD 100), Ignatius of Antioch (died around AD 115), Polycarp, Bishop of Smyrna (born around AD 69, died around AD 155), and Papias of Hierapolis (born around AD 70, died around AD 130/140). It was their endeavour to defend the Christian faith against both Gentiles and Jews, and to protect the fundamentals of the Christian doctrine.
One of the defining personages for the church was Athanasius the Great (around AD 295 to AD 373), under whose influence the Nicene Creed was formulated in the year AD 325.