Irenaeus was a second-century Greek bishop who served in Lugdunum, the city known today as Lyon. Born in Smyrna, he was a student of Polycarp and played a vital role in shaping early Christian theology. He is most famous for his efforts to defend orthodox beliefs against various Gnostic interpretations of scripture. By emphasizing the importance of apostolic tradition and the four canonical gospels, he helped establish foundational theological frameworks that guided the growing Christian communities in Gaul and beyond.