Irenaeus, Saint (A.D. 130?–202?), important theologian and leader during the 2nd century A.D. Born in Asia Minor, Irenaeus is thought to have served as a missionary to southern Gaul and as conciliator among the churches of Asia Minor that had been upset by heresy. A strong opponent of Gnosticism, a spiritual movement that took up pagan, Jewish, and Christian forms, Irenaeus attacked the movement in his preeminent work, Against Heresies. Irenaeus upheld the validity of the Old Testament, as well as of several writings that were destined to become part of the New Testament. He became the Bishop of Lugdunum, which is now Lyon, France, in about A.D. 177.
See also: Theology.