Irenaeus was born in the 2nd century A.D. During a time when others converted as adults, Irenaeus was raised as a Christian.

He became a piest and then Bishop of Lyon. His writings emphasized the importance of early church traditions and apostolic succession.

Irenaeus also focused on unity by encouraging all Christians to follow the same theological doctrine. He challenged the growing belief of salvation by knowledge, or Gnosticism.

During a time when the Gospels of Matthew, Mark, Luke, and John varied in popularity and reverence, Irenaeus established all four as canonical scripture.