The Bible makes it clear concerning the reality of demons and or evil spirits.
Yet there is no information in the Bible regarding their origin. Although Scripture does not tell us specifically where they came from, there are many theories as to where they came from. Here are 4.
1. Disembodied Spirits of a Pre-Adamic Race
A popular theory is that the demons are disembodied spirits of some race that existed before Adam, A race of people who were destroyed by God because they were so evil. These could be spirit-beings that are separate from fallen angels. It is believed that demons existed at another place and time in bodily form, but are now disembodied spirits looking for bodies to possess. This could be so, but there is no scripture reference at all to it.
2.Fallen but not Confined Angels
Some believe with respect to the identity of demons, is that they are “fallen angels.” Some of the angels who fell were bound while others became demons. These angels are doing the bidding of Satan by causing evil and possessing human beings. Satan, the ruler of the angels, is also called the ruler of the demons. I don’t subscribe to this one because they are a separate created being by God and I don’t think they changed their psychical state after the fall.
3. Spirits of the Evil Dead
Some feel that demons are the disembodied spirits of the evil dead – they are wandering around the realm of the dead seeking bodies to inhabit. This view has no biblical support. It is contradicted by the story the Lord told of the rich man and Lazarus. When the rich man died, he was in the unseen world in a place called Hades awaiting judgment. He was also told that he could not go back to this world. So I reject this one completely. This could also be thought of as kind of a purgatory which is what the Catholics believe and that evil spirit can be prayed for, redeemed, and bought out of by their earthly relatives. This one is ludicrous.
4. Offspring of Angels and Earthly Women
There is the view that holds the demons resulted from the relationship between angels and earthly women. The demons did not exist before this point. This view takes Genesis 6 as referring to the unlawful marriages between fallen angels and human women. Their offspring was the Nephilim whom some believe to be half-human, half-angelic.
I personally believe in a combination of 1 and 4 leaning more to number 4, the offspring called the Nephilim, the giants of Genesis 6. The Israelites fought these giants, the Philistines, and the best account is David slaying Goliath. At the time of Noah when God destroyed all life except for those of Noah’s family and the animals on the boat, these hybrid humanoids were destroyed. Where did the spirit of those go to? I believe they are some of the demons and they wander around looking for something to inhabit. Scripture reference is as follows:
Matthew 12:43-45 (43) When the unclean spirit is gone out of a man, he walketh through dry places, seeking rest, and findeth none. (44) Then he saith, I will return into my house from whence I came out; and when he is come, he findeth it empty, swept, and garnished. (45) Then goeth he, and taketh with himself seven other spirits more wicked than himself, and they enter in and dwell there: and the last state of that man is worse than the first. Even so shall it be also unto this wicked generation.
It really does not matter where they came from. It matters that they are real and here to cause as must havoc as they can. The nit pickers and unbelievers can argue to hell freezes over and of course that will never happen.
See Principalities, Powers and Spiritual Wickedness in High places for a detailed explanation of how Lucifer and his Evil Spirits operate.
You can also glean info of their origin by them boasting and the names they take on: Demon Names and how to Identify them