From the Greek daimon, or spirit, demons are powerful supernatural beings without the dignity of gods. Ancient demons could be good or bad. Traditionally demons have been said to reign on some other plane, usually some form of hell, and are creatures of fire.

The classical Greek demon, Pan, was a nature spirit. Other demons protected homes, fields, or travelers. Malevolent demons brought on disease or insanity. Hebrew and Christian culture considered all demons evil. In 1589, a leading expert named Brinsfield listed major demons and their specialties. These included: Lucifer, pride; Satan, anger; Beelzebub, gluttony; and Belphegor, sloth.

http://en.wikipedia.org/wiki/List_of_demons