Irenaeus of Lyon

Bishop of Lyon (c. 130-202) — the first systematic theologian of the Church; author of Against Heresies.

St. Irenaeus of Lyon is the first comprehensive systematic theologian of the Christian Church: his Against Heresies is the earliest extant systematic refutation of Gnosticism and the first attempt to articulate the whole of Christian theology in a unified framework. His theology of recapitulation (anakephalaiosis) — Christ re-running and redeeming every stage of human existence — became foundational for Orthodox soteriology. His insistence on apostolic succession and the rule of faith as criteria of orthodoxy shaped the Church's self-understanding.