The Temptation of Christ 1854 (wikipedia)

The roots of demonology are nearly impossible to trace.  A brief study of world religions both current and past turns up a variety of malevolent beings that behave in similar ways to how Christians perceive demons.  It is known for example that the grimoires, books of magic, used in Babylon and Sumeria refer to evil spirits that cause disease and other ills.  These texts also contained spells for driving them off and recommendations of ways to ward them off.  While this is the earliest written example of demonology it can also be reasonably inferred that traditions of malevolent spirits that were not of human origin go back even farther.  Beliefs found both among the Native Americans and   in Africa reference evil spirits that interact with human beings up to and including possession.
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This is more video from our trip to GhoStock 7 back in April. Unfortunately we weren’t able to snag Mr. Zaffis for an interview but we did get a pretty good chunk of his lecture. He discusses everything from possession, oppression, getting into the field, his uncle Ed Warren, the Haunting in Connecticut, plus some other cool stuff like buddhist exorcists. Oh, and please excuse the shoddy camera work, it was filmed downstairs in the library at the Hawthorne Hotel. And it was wicked daaaaaark.

For more info on John Zaffis.