The word Demon derives from the Greek term Daimon and means simply a spirit of some kind - not necessarily a bad one. However, the word has acquired a distinctly negative connotation since then. Nowadays, most people use the word Demon to refer to evil, hellish spirits or beings. Some religions describe Demons as "Fallen Angels", i.e. Angels who rebelled themselves against God.
The demons were the heavenly angels of God that were created on the second day of creation (in Genesis book) about 350 thousand angels lived in the celestial kingdom serving the throne of God. During the creation of man and the new paradise on earth, Lucifer (the primary consented angel of God, prince of the cherubim) created a jealousy about Adam, using all his hidden wickedness, resulting in the expulsion of Adam and Eve in paradise, back to the kingdom heavenly, he decided to covet the throne of God, wanting to replace their leadership plan and domination. Archangels Michael and Gabriel were the keepers of the throne of God, Lucifer manipulated 200 thousand angels guilds: archangels, cherubim, seraphim and throne to help him with his plan in exchange for much power, but the 150 thousand angels were against, with a separation, these angels Michael and Gabriel warned about the plans of Lucifer and his 200 thousand followers, Miguel climbed into the high plane of God and informed of evil and Lucifer riot, the consent of him to take the throne. God commands Michael and Gabriel prepare for the celestial battle, God and the 150 thousand righteous angels fought against the opposition of the other angels wanting to invade the throne, Lucifer becomes a dragon to reach God the size to destroy it, God and righteous angels defeat Lucifer and his followers with a three-dimensional hole, playing all in mount Hermon in the earth, but the evil of the fallen and expelled from the heavenly kingdom angels, aggravated further by teaching and practicing the wickedness of man was defiled because of them, God ordered Michael and his army of archangels to hunt the 200 thousand fallen angels on earth, pulling his wings and playing in three-dimensional hole underworld of hell, eternal prison. (Book of Enoch), the course of time the demons embody or appears temporarily to bring terror and scamming people, starting a hatred of God's creation.
Demons and angels share the same power (transmorfy, telekinetic and telepath), they have the ability to turn into anything, but without the wings also, the demons lost their brightness, using their darkness, but the power of light heavenly is their weakness. Much of the time, the demons create synthetic wings like bats and even locusts, with reddish fur, standing goat and horns and scorpion tails, they used these forms in their bodies to torture the dead, but then return in its original form as angels.
They have been most often portrayed as horned humanoids, usually small ones - but can also assume several forms depending on the work they appear in. They are also typically capable of possessing Humans, as well as other species, objects and even locations.
Many species in science fiction are referred to as demons, resemble the mythological interpretation of a demon, or are in fact some form of demon or demonic entity: