Irenaeus is regarded by some as the founder of apologetics. He was a 2nd Century Bishop of Lyons and was the first great theologian of the patristic age. His most renowned work, Against Heresies, is a defence of the orthodox Christian faith and an attack on the heresies of the day. Irenaeus was resolute in his beliefs but in his style of reasoning he actively sought to persuade and convince people of the truth.