Irenaeus of Lyon

Irenaeus grew up in Asia Minor, where as a boy he heard Polycarp of Smyrna, and became bishop of Lyon in Gaul after the persecution of 177. His five books Against Heresies, written around 180, attack Valentinian and other Gnostic teachers and describe their systems in detail.

He gives the earliest explicit statement that there are exactly four Gospels and names their authors, appeals to the succession of bishops in Rome and elsewhere as a guarantee of apostolic teaching, and develops a theology of Christ recapitulating humanity. Much of what is known of second-century Christianity comes through him.