Gnosticism
Gnosticism (after gnôsis, the Greek word for "knowledge" or "insight") is the name given to a loosely organized religious and philosophical movement that flourished in the first and second centuries AD.[Citation Needed] Though the exact origins of this school of thought cannot be traced with any certainty, it is possible to infer that certain non-canonical sources dating from the first and second centuries BC.
There are numerous references to the Gnostics in second century proto-orthodox literature. Most of what we know about them is from the polemic thrown at them by the early Church Fathers.[1] Marcion was the most famous of the Gnostics, and he established a "canon" of the Pauline epistles that did not include the pastorals and a "mutilated" Luke. Justin Martyr mentioned Marcion c. 150 CE, and Irenaeus and Tertullian wrote against him extensively in the late second century (in Against Heresy and Against Marcion, respectively).[2]