This URL (http://www.gotquestions.org/Satan-fall.html) has a ton of information with Scripture references. I recommend going there to start your own research.
The Bible clearly states that Satan was one of God's most prestigious angels before he fell from Grace. He lost his eligibility for grace because he was prideful and wanted to be God.
I would recommend starting with Isaiah 14 and reading that chapter. The problem with man made theology is that it can easily distort God's word. If the church or Christian denomination you belong to doesn't preach from the Bible, I would use a high level of discernment.
We'd like to believe that all Christian pioneers are 100% faithful to the Lord, but that's not possible, and generally untrue. Ever heard the phrase wolves in sheep's clothing?