Irenaeus was a Greek who was born between the years 120 and 140. He had the great privilege of being taught by St. Polycarp, who had been a disciple of St. John the Apostle. Irenaeus once told a friend: "I listened to St. Polycarp's instructions very carefully. I wrote down his actions and his words, not on paper, but on my heart."
After he became a priest, Irenaeus was sent to the French city of Lyons. It was in this city that the bishop, St. Pothinius, was martyred along with a great many other saints. Irenaeus was not martyred at that time because he was asked by his brother priests to take an important message from them to the pope in Rome. In that letter they spoke of Irenaeus as a man full of zeal for the faith.
When Irenaeus returned to be the bishop of Lyons, the persecution was over. But there was another danger: a heresy called Gnosticism. This false religion attracted some people by its promise to teach them secret mysteries. Irenaeus studied all its teachings and then in five books showed how wrong they were. He wrote with politeness, because he wanted to win people to Jesus. However, sometimes his words were strong, such as when he said: "As soon as a man has been won over to the Gnostics, he becomes puffed up with conceit and self-importance. He has the majestic air of a rooster who goes strutting about." St. Irenaeus' books were read by many people. Before too long, the whole heresy began to die out. St. Irenaeus died around the year 202. Many believe he was martyred.
"It is better and more profitable to be simple and less well educated but close to God through charity than to appear wise and gifted but to blaspheme the Master." -St. Irenaeus