In religion, demon is a minor supernatural being, sometimes in the service of a more powerful god. The word comes from the Greek daimon ("spirit," "genius," and sometimes "power"). A demon's attitude toward mankind may be good, neutral, or evil.
In many religions, including some that are modern as well as most that are associated with primitive folk cultures, demons are thought to inhabit the forces and objects of nature, such as lightning, fire, rivers and trees. The souls of the dead, particularly those ancestors, are also believed to be demons. Special sacrifices are made to the demons in order to persuade them to do good, rather than evil. Good demons act as the guardians of wells, tombs, houses, and even entire communities. Evil demons not only are responsible for misfortune, but are believed capable of entering the human body and causing disease or madness. Charms and amulets are worn to prevent such entries. If these fail, elaborate and sometimes dangerous rituals are performed to exorcise, or drive out, the evil demon.
In Jewish, Christian, and Islamic tradition good demons became known as angels, who serve as messengers of God, and evil demons became known as devils, who serve the supreme evil being, the Devil. For example, the serpent who tempts Eve in the Garden of Eden in the Old Testament story is regarded as a subordinate devil or as the Devil himself.
Many peoples have envisioned demons in myths and folktales, where they often have a grotesque but human form. Demons appear as the trolls and ogres of Scandinavian legends, the pixies and giants of Germany, the leprechauns of Ireland, and the jinns, or genies of the Arabs. Demons may also take on the form of fantastic animals, such as werewolfs, vampires, mermaids, and swan maidens. In China, foxes are sometimes thought to change into beautiful women.