Where Did Evil Spirits Come From?

An evil spirit (or demon) is not the
same as a fallen angel; it is actually
the offspring of a fallen angel. When
fallen angels took to themselves
human wives (Genesis 6:1-2), the
children born to them became mighty
giants, corrupting the human race
and accelerating wickedness to such a
degree that God saw it necessary to
destroy all flesh with a Great Flood,
saving only the righteous man Noah
and his family.
When the mortal bodies of these
angel-human hybrids died, their
immortal spirits roamed the earth
seeking human bodies to harass and
indwell. The male ones are
malevolent spirits and the female
ones are seductive spirits. These
continue to afflict the human race
even now. They know the weaknesses
and desires of mankind, for they once
experienced a human body.
Unlike fallen angels, who can appear
in bodily form, evil spirits must inhabit
a body (either human or animal). An
example of this is when Jesus cast out
the legion of demons from a man and
sent them into a herd of pigs (Luke
8:27-35). Both fallen angels and evil
spirits serve their master Satan in the
kingdom of darkness.