There's a Good Book about goodness and how to be good and so forth, but there's no Evil Book about how to be evil and how to be bad. The Devil had no prophets to write his Ten Commandments, and no team of authors to write his biography. His case has gone completely by default. We know nothing about him but a lot of fairy stories from our parents and schoolmasters. He has no book from which we can learn the nature of evil in all its forms, with parables about evil people, proverbs about evil people, folklore about evil people. All we have is the living example of people who are least good, or our own intuition.
Very few people believe in the devil these days, which suits the devil very well. He is always helping to circulate the news of his own death. The essence of God is existence, and He defines Himself as: 'I am Who am.' The essence of the devil is the lie, and he defines himself as: 'I am who am not.' Satan has very little trouble with those who do not believe in him; they are already on his side.