Irenaeus lived from around 125 to 202 AD and was Bishop of Lyons in southern Gaul (now Lyons, France). He wrote a massive five-volume work, Against Heresies, toward the end of the second century. In responding to the false teaching of the gnostics, Irenaeus produced one of the first and most significant works defending what God has revealed in Scripture.
While I would love to provide extended quotes from Against Heresies (which you can read in its entirety online!), I will simply whet your appetite for more by this insightful quote from the beginning of his work:
"Error, indeed, is never set forth in its naked deformity, lest, being thus exposed, it should at once be detected. But it is craftily decked out in an attractive dress, so as, by its outward form, to make it appear to the inexperienced (ridiculous as the expression may seem) more true than the truth itself" (1.1.2).