St Irenaeus was a disciple of Polycarp,who in turn was a disciple of John the evangelist; so in a way, Irenaeus was a spiritual grandson of John. He was born about the year AD 130 and after he converted he became a deacon and priest. Eventually he became bishop of Lyons in France and was martyred about the year AD 200.
_Irenaeus was one of the early "apologists" men who wrote in defense of the faith and his greater work was "Against the Heresies." If you study theology it is utterally amazing how often this work is quoted as an authority.
Irenaeus was clear and concise about Christian teaching. He was able to demonstrate truths from scripture and in a logical, reasoned fashion. He as probably the first of the great Catholic theologians and philosophers.