[thinktwice]

When, where, why, and from whom did the concept "demon" originate?

You've missed the point in my question. Let's start again with just one question. When did the concept "demon" originate in history?

I'd guess that the mental state associated with "demonic possesion" has been with mankind for countless milleniums, but when did that state become associated with the devil?

The Devil -- there's another concept that must have some history, too. The Bible, perhaps?

[GeekDejure]

The Devil -- there's another concept that must have some history, too. The Bible, perhaps?

Umm. . . The Koran, perhaps?

.

[Cvengr]

Scripturally, Job, the oldest book of Scripture has references to Lucifer, Satan, angels and fallen angels.

Demonic possession may be more than a mental state.

Devil as a device of evil independent of God's will.