The tale that the devil was originally an angel, even the brightest most glorious, and highly placed angel in Heaven, is a late developement in religous legend. Partly is was based on a passage in Isaiah "How art thou fallen from Heaven, O Lucifer, son of the morning, how are though cut to the ground, which didst weaken the nations! For thou hast said in thine heart, I will ascend into Heaven, I will exalt my throne above the stars of God: I will sit on the mount of the congregation in teh sides of teh north: I will ascend above the heights of the clouds; I will be like the Most High. Yet thou shalt be brought down to Hell, in the sides of the pit (Isaiah 14:12-15)." Asimovs Annotated Paradise Lost