Question: What demon from Assyrian and Babylonian mythology is battled by Father Damien Karras in "The Exorcist" film series? 
Sentence (from "Lankester Merrin"): Merrin does not appear again until much later in the novel, when he joins the protagonist, Father Damien Karras, in Washington, D.C. to exorcise the demon from the body of a young girl.
Relevant evidence: Yes