Irenaeus of Lyon
Approx. 125 AD — Approx. 202 AD · Feast day: June 28
Born in Smyrna and schooled at the feet of Bishop Polycarp — who had known the Apostle John — Irenaeus of Lyon became the second century's great bulwark against Gnosticism, writing the first comprehensive defense of orthodox Christian doctrine. When his predecessor died a martyr, Irenaeus took up the bishop's staff and held the Church of Lyon together against heresy, persecution, and division.