(Repost from previous WordPress blog.)
St. Irenaeus, a Bishop in Lyons, was taught and influenced by St. Polycarp, the Bishop in Smyrna, who himself was the personal disciple of the Apostle John.
St. Ignatius was the personal disciple of the Apostle John, and was appointed to his post as Bishop of Antioch by the Apostle Peter himself. He was martyred for the faith.
St. Cyprian was an adult convert and became Bishop in Carthage. He was martyred for the faith.
St. Augustine, Bishop of Hippo, was so influential that he is known today as the "Father of Western Christianity."