Adrian,
The devil is a loser, not a contender. The noted Puritan theologin Jonathan Edwards describes him as a “blockhead” for even thinking he can defeat God. His fate is already sealed, yet he continues to rebel strenuously against God. However, he is, for the time being, still “the ruler of this world”, and as long as we are alive on this earth he poses a very real threat to us and demands our caution.
John 16:11 and concerning judgement, because the ruler of this world has been judged.
I can see this question and answer routine going on for some time. Trust me, coming up with questions, especially about the devil, is far easier than coming up with answers. So, if you are genuinely interested, I would suggest first the Bible. Not just any Bible, but a Reformed Study Bible. It would provide some answers, but I would caution you to take everything in its context (which can be succinct to vast), and not to try to read something into it that isn’t there. The major things are easy to find and understand, and they are repeated, often. The minor things, are not. The Bible is its own best interpreter. Just remember, there is more wisdom in the Bible that any one man can fathom.
Also, there are many counterfit bibles (small “b”), used by cults. Don’t be fooled. or waste any time reading them. They are erroneous.
Plan B would be to read books written by the men who study and teach the Bible for a living; ordained preachers. If you are interested in the world of fallen angles then, I would recommend The Invisible War by Donald Grey Barnhouse (ISBN 0-310-20481-X). Just be sure you recognize the difference between Scripture truth, and man’s speculation.
Finally, a warning. Don’t get too engrossed in devils, demons and the like. The more interest you have in them, the more interest they are likely to have in you. Play it safe; take what the Bible reveals, and nothing more.
Dueteronomy 29:29 The secret things belong to the Lord our God, but the things revealed belong to us and to our sons forever, that we may observe all the words of this law.
1 Peter 5:8 Be of sober spirit, be on the alert. Your adversary, the devil, prowls around like a roaring lion, seeking someone to devour.