Demons are supernatural, often vicious, prevalent in religion, mysticism, literature, fiction, mythology, and folklore.

In ancient Near Eastern religion and Abraham's tradition (including ancient and medieval Christian Demonology), demons are regarded as harmful spiritual entities, which may cause demons to attach themselves under the sky level, so they need to be exorcized. In Western mysticism and Renaissance Magic, because of the combination of Greek Roman magic, Jewish agada and Christian demonology, the devil is considered to be a spiritual entity that can be called and controlled.

Psychologist Wilhelm Wundt said: "in the world myth attributed to the devil's activities, the harmful devil dominates, so in the general concept, the age of the bad devil is significantly older than the good devil." Sigmund Freud put forward this idea and claimed that the concept of devil originated from the important relationship between the living and the dead: "in fact, the fact that devil is always regarded as the soul of the latest dead is better than any mourning. About the origin of demon belief. "

M. Scott peck, an American psychiatrist, has written two books on the theme of liars: the hope of curing human evils and Demons: a psychiatrist's personal description of possession, Exorcism and redemption. Peck detailed several cases involving his patients. In the liar, he provides the identification characteristics of evil characters, and he classifies him as a character disorder. In the devil's glimpse, peck describes in detail how he is interested in Exorcism in order to expose the possession myth of evil spirits; only after encountering two cases that are not suitable for psychology or psychiatry can he be persuaded. Parker concluded that possession is a rare phenomenon related to evil, and that the possessor is not actually evil. Instead, they are fighting evil.