Anatolian-born theologian Irenaeus, in his youth a disciple of Saint Polycarp of Smyrna, later serves as bishop of Lugdunum (Lyon) in Gaul.

A man of peace and of tradition, he devotes his major efforts in combating gnosticism, writing his great work, Adversus haereses (Against Heresies), to this end.

In opposition to the teachings of gnostics such as Basilides and Valentinus, Irenaeus develops the doctrine of recapitulation (anakephalaiosis) of all things in Jesus Christ.

A champion of the apostolic tradition, Irenaeus works to systematize the religious and theological traditions of the church.

As a participant in the Quartodeciman controversy over the date for the observance of Easter, Irenaeus argues for diversity of practice in the unity of faith.

Dying around 202, Irenaeus leaves several extant works (later Christians regard him as the father of Catholic theology).