Irenaeus (c. 115–202) was bishop of what is now Lyon, France. He was a disciple of Polycarp, who himself was a disciple of the Apostle John. Born in the first half of the second century (the exact date is disputed: between 115 and 125 according to some or 130 and 142 according to others), Irenaeus is thought to have been a Greek from Polycarp's hometown of Smyrna in Asia Minor, now Izmir, Turkey. He was raised in a Christian family.

Irenaeus wrote a number of books, but the most important that survive are the five-volume Adversus Haereses ("Against Heresies"). If Irenaeus was Greek he would probably have written in Greek. Only fragments of the original Greek text exist, but a complete copy exists in Latin along with an Armenian translation of Books IV and V.

The Gnostics produced a large volume of "other gospels" and Irenaeus weighs in on those:

But it is not possible that the Gospels can be either more or fewer in number than they are. For since there are four zones of the world in which we live, and four principal winds, while the church has been scattered throughout the world, and since the "pillar and ground" of the church is the Gospel and the spirit of life, it is fitting that she should have four pillars, breathing incorruption on every side, and vivifying human afresh. From this fact, it is evident that the Logos, the fashioner [demiourgos] of all, he that sits on the cherubim and holds all things together, when he was manifested to humanity, gave us the gospel under four forms but bound together by one spirit. (Against Heresies 3.11.8)

Irenaeus cites from most of the New Testament canon, as well as the noncanonical works 1 Clement and The Shepherd of Hermas; however, he makes no references to Philemon, 2 Peter, 3 John or Jude.