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 (film)
Lankester Merrin, a veteran Catholic priest who performed an exorcism in the 1950s, is on an archaeological dig in the ancient city of Hatra in Iraq. There he finds an amulet that resembles a statue of Pazuzu, a demon of ancient origins with whose history Merrin is familiar.
In Georgetown, actress Chris MacNeil is living on location with her 12-year-old daughter Regan; she is starring in a film about student activism directed by her friend and associate Burke Dennings. After playing with a Ouija board and contacting a supposedly imaginary friend whom she calls Captain Howdy, Regan begins acting strangely, including making mysterious noises, stealing, constantly using obscene language and exhibiting abnormal strength. Chris hosts a party, during which Regan comes downstairs unannounced, tells one of the guests—an astronaut—that he will die in space and then urinates on the floor. Later, Regan's bed begins to shake violently, adding further to her mother's horror. Chris consults a number of physicians, but Dr. Klein and his associates find nothing physiologically wrong with her daughter, despite Regan undergoing a battery of diagnostic tests. 
One night when Chris is out, Burke Dennings is babysitting a heavily sedated Regan. Chris returns to hear he has died falling out the window. Although this is assumed to have been an accident given Burke's history of heavy drinking, his death is investigated by Lieutenant William Kinderman. Kinderman interviews Chris. He also consults psychiatrist Father Damien Karras, recently shaken after the death of his frail mother.