Originally from Asia Minor, a disciple of Saint Polycarp, he came to the West on an unknown date (before 177) and became the second Bishop of the Church of Lyon, after Saint Pothinus who was martyred in 177. He remained a Bishop until his death, around 200. He had stayed in Rome and, around 190, addressed Victor of Rome to settle the dispute that had arisen over the date on which Easter should be celebrated.
A great theologian, he was the author of the first attempt to write an organised and reasoned account of the Christian faith as a whole. He opposed the heresies of his time, particularly Gnosticism, which he described and refuted at length before expounding the faith of the Great Church.
His work, written in Greek, is transmitted mainly in Armenian and Latin versions. Two works are preserved: Against the Heresies (in 5 books) and Demonstration of the Preaching of the Apostles (a short biblical catechism).