The decisive shift to Christianity occurred in 655 when King Penda was slain in the Battle of the Winwaed and Mercia became officially Christian for the first time. In the end, it was the conversion of the Anglo-Saxons to Roman Christianity that incorporated the British Isles within the religious, political, and economic structures of European Christendom
First, a bit of a disclaimer: Religion is as complicated as the people who follow it. Taking on even a small section of theology is a massive undertaking, and honestly, it's just a mess of different versions of all kinds of stories and beliefs. So that being said, let's talk about some of the bad boys of several religions: fallen angels.