Demon
The contemporary Roman Catholic Church unequivocally teaches that angels and demons are real beings rather than just symbolic devices. The Catholic Church has a cadre of officially sanctioned exorcists which perform many exorcisms each year. The exorcists of the Catholic Church teach that demons attack humans continually but that afflicted persons can be effectively healed and protected either by the formal rite of exorcism, authorized to be performed only by bishops and those they designate, or by prayers of deliverance, which any Christian can offer for themselves or others.
The Exorcist
In "Angel: Earthly Possessions", a spin-off comic story based on the TV series "Angel", protagonist Angel finds himself dealing with a priest who performs exorcisms, but comes to realize that the priest is summoning the demons for him to exorcise in the first place. He also makes a note of "The Exorcist" film, noting that the vision it created of possession actually made things easier for possession demons by making it harder for humans to know what to expect from a possession.