Who (or what) are the Shadow-Beings?

This book has been written on the subject of the Shadow-Beings. Included here are many statistics, theories and ideas, what history has to say about these "shadow-beings". I have written 2 books prior to this when I was a lot younger, the first was an account of my own experience, the second included stories shared by reader's, as to their own encounters & experiences. And, now with my last effort & contribution, included here are theories, and most importantly comparisons as for those who share this common experience.