Irenaeus was a Greek who was born in Asia Minor. He was blessed to be taught by St. Polycarp of Smyrna, 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. Irenaeus was asked to go on a mission 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.
While Irenaeus was away, the harassment of Christians began in the city of Lyons. The bishop, St. Pothinius, was killed along with a great many other saints who died as martyrs for their faith in Jesus.
When Irenaeus returned the persecution was over and he was made bishop of Lyons. But now there was another danger: false teachings about the Catholic faith called Gnosticism. This false religion attracted some people by its promise to teach them secret mysteries.
Irenaeus studied all its teachings and then wrote five books showing how wrong they were. He wrote with politeness, because he wanted to win people to Jesus. However, sometimes his words were strong, like: "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 and soon people began to ignore the Gnostics teachings. St. Irenaeus was killed around the year 202 dying a martyr for Jesus.
"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