The Church in the New Testament was Established sometime in the first century, but towards the end of the second century started to Apostatized. By 350 AD had become the beginning of the Catholic Church.
For more on this read Catholic Church and New Testament, on the bottom Navigation bar.
The Adversary is always at work, and will always be as long as Earth stands.
The Adversary first made his appearance in the Garden of Eden as the Serpent, tricking Eve into taking a bite from the fruit of the Tree of Good and Knowledge, then Eve having Addam, to take a bite, which they were told by God not to do, for that God expelled them from the Garden of Eden.