The term "demons" was not always understood to have the absolutely negative connotation that it does today. Homer used the terms "demons" and "gods" more or less interchangeably. Another opinion was that demons were intermediaries between men and gods, and that demons had once been men. Plutarch speaks of "human souls as commencing, first heroes, then demons, and afterward as advancing to a more sublime degree." Philo of Byblus seems to draw on this same tradition when he states that, "The most ancient of the barbarians, especially the Phoenicians and Egyptians, from whom other people derived this custom, accounted those the greatest gods who had found out things most necessary and useful in life -- and had been benefactors to mankind."
Our current use of the term "demon" is to denote a malignant spirit, and comes to us primarily form New Testament writers. However, there is still uncertainty as to whether or not demons are considered to be distinct and separate from the Devil and his fallen angels.
Demoniacal Possession
Demon possession - that is, a human who has become inhabited or "taken over" by a demon and who cannot, consequently, exercise his own will - is noted in the New Testament, specifically in Mark, Chapter 5, ver. 12. Josephus also mentions a method of exorcism prescribed by Solomon, which had "prevailed or succeeded greatly among them down to the present time." Unfortunately, Josephus does not describe the method used.
There is little doubt that most of what was described in older times as "demon possession" would today be diagnosed as some sort of mental illness, and treated accordingly. Nevertheless, a few cases of possession do seem to crop up from time to time, and the Roman Catholic Church does continue (sparingly) to perform exorcisms.
Periods of Increased Demon Activity
Some historians of times past believed that there were cycles during which demonic activity increased, and used this