Saint Irenaeus is one of the Pillars of Truth in the Church. He was born in Asia Minor in about AD 125. This time and place were still permeated with the teachings and power of the Apostles themselves, and was led by the immediate disciples of the apostles. He was well versed in the texts of Holy Scripture, and is known to have learned much of Greek philosophy.
There had been for quite some time established trading routes between Asia Minor and the Marsailles/Lyons area of present day France, and due to this association, Irenaeus was sent as a priest to Lyons to serve the vigorous Christian Church established under Bishop Pothinus, another oriental (Asia Minor) like Irenaeus.
Irenaeus' high regard amongst the clergy of Lyons shows, when he was sent to Rome on behalf of the Church in Asia Minor. At this same time, the great persecutions of the Catholic faithful at the hands of both Romans and pagans suffered the Church at Lyon, Rome, and in Asia Minor. Montanism - one of the many gnostic and semi-gnostic heresies - had implanted itself in the Churches of Asia Minor, and a "most religious and orthodox" letter was given to Pope St. Eleutherius by Irenaeus pleading for leniency in dealing with the Montanist brethren in Phrygia. During Irenaeus' time in Rome, Pothinus and many others were martyred in Lyons, and the Saint was sent back to Lyons to fill the vacant See.
By the time of his arrival, the persecution had stopped, and his tenure as Bishop of Lyons was one of relative peace. In addition to his pastoral duties, he is known to have evangelized the neighboring lands, and he was also forced to deal with the preponderance of gnostic heresies emerging in the name of or separate from Christ throughout Gaul.
He wrote in Greek (then it was quickly translated to Latin) a five volume exposition of Christian truth where the doctrines of the numerous gnostic sects were presented, then contrasted with the teachings of the Apostles and the Holy Scriptures. He intended to "strip the fox" as he stated, removing the veil of secrecy surrounding gnosticism. It was a well circulated set of texts, and did much to vanquish [but not irradicate, as we see gnosticism appear today], gnosticism in the Church of Christ. He is thought to have died in about 203.