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.
Satan
Most early Christians firmly believed that Satan and his demons had the power to possess humans and exorcisms were widely practiced by Jews, Christians, and pagans alike. Belief in demonic possession continued through the Middle Ages into the early modern period. Exorcisms were seen as a display of God's power over Satan. The vast majority of people who thought they were possessed by the Devil did not suffer from hallucinations or other "spectacular symptoms", but "complained of anxiety, religious fears, and evil thoughts."