The book of Enoch would agree that the offspring of the watchers (angels assigned to look after Adamic men) and women are the demons, i.e. that their bodies were destroyed in the Noah flood but their spirits continued to roam the earth, e.g.:
And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day. - Jude 1:6
God's Name is I AM.
Not the original watchers, but others of their stature. J.R. Tolkien understood this to be true, hence by the close of the Silmallion, Morgoth (Lucifer) has been banished to outer darkness. By the start of the trilogy, Sauron-—a second level angel and Morgoth’s commander-in-chief so to speak-—takes up where Morgoth left off.
Lucifer’s legion is 1/3 of the pure spirit hierarchy. Those who are in chains are but a fraction of it.