It is said that he is a fallen an angel. He was and angel in heaven but was kicked out of heaven.
Revelation 12:9>And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.
http://www.bible.org.nz/articles/the-devil-and-his-angels.html
The link above explains as well.