Devil - The Devil is the name given to a supernatural entity who, in most Western religions, is the central embodiment of evil. This entity is commonly referred to by a variety of other names, including Satan, Asmodai, Beelzebub, Lucifer and/or Mephistopheles. In classic demonology, however, each of these alternate names refers to a specific supernatural entity, and there is significant disagreement as to whether any of these specific entities is actually evil. (wikipedia)

The Devil of the New Testament and Christian theology is an evil personality, ruling over a kingdom of evil spirits, the inveterate foe of both God and man; a fallen angel, one of the celestial host who rebelled against God and was cast out from heaven.(The Society)

In Jewish and Christian theology, the prince and ruler of the kingdom of evil; any subordinate evil spirit.