Irenaeus

Saint Irenaeus of Lyons (c. 130–202 AD) is best known as a foundational second-century Christian bishop and theologian who famously defended orthodox Christianity against Gnosticism in his monumental work Against Heresies. He also provided vital early testimony on the fourfold Gospel canon and apostolic succession. Wikipedia +6

Key Contributions and Writings

• Against Heresies (Adversus Haereses): A massive five-book treatise exposing and refuting Gnostic systems, which claimed secret spiritual knowledge and rejected the physical world. Logos Bible Study Platform +3
• The Four Gospels: Irenaeus was a primary early voice who insisted on the authority of precisely four Gospels (Matthew, Mark, Luke, and John). Saint Irenaeus Catholic Church
• Recapitulation Theory: He taught a theology of salvation where Christ ("the new Adam") retraced and reversed humanity's disobedience, summing up human history to redeem it. Reddit·r/Catholicism
• Apostolic Link: As a disciple of Polycarp (who knew the Apostle John), Irenaeus served as a crucial bridge connecting the generation of the Apostles to the wider early Church.