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)
Both priests witness Regan perform a series of bizarre, vulgar acts. They attempt to exorcise the demon, but the stubborn entity toys with them, especially Karras. Karras shows weakness and is dismissed by Merrin, who attempts the exorcism alone. Karras enters the room later and discovers Merrin has died of a heart attack. After failing to revive Merrin, the enraged Karras confronts the mocking, laughing spirit, and wrestles Regan's body to the ground. At Karras's invitation, it leaves Regan's body and possesses Karras. In a moment of self-sacrifice, the priest throws himself out of the window before being compelled to harm Regan. He is mortally injured. Father Dyer, an old friend of Karras, happens upon the scene and administers the last rites to his friend.