Christianity has a lot of fanfiction, and large chunks of it have been merged with the canonical scripture in the popular imagination. Ever noticed how the devil doesn't actually feature in the bible anywhere? Yeah.
Oh there are lots of references to "satan," but what is he? God's opposite number? A fallen angel? A non-fallen, benign angel? Man's own sinful nature? Previously popular pagan entities? It's a long way from the modern theological concept of the devil.
Since then we have post-rationalised all these vague biblical references into one guy with horns and goats feet who hangs out in a lake of fire, but that is a (comparatively) recent idea, as you will find if you examine your own wiki link a little more closely. (BTW the lake of fire barely gets half a sentence either. That's also very much something that came with the "expanded universe" books. Actually they were paintings rather than books, but you can look that up for yourself.)
Wait until you hear about god's first attempt at woman, Eve's predecessor, who went bad! There's a lot of fun stuff that modern christianity has chosen to throw out.
http://en.wikipedia.org/wiki/Biblical_apocrypha