There are two main types of demons: those who are aware they are demons, who are awakened in evil and for evil, and those who are not aware they are demons, who are asleep.

"Millions of women and distinguished gentlemen, who are presently living on this world, do not have their Innermost (Spirit), and are therefore perverse demons, even though they still have physical bodies. The human being becomes a demon when the psychological “I” attains absolute control of the four bodies of sin (physical, ethereal, astral and mental), then the Innermost (the Spirit) withdraws from him... When somebody who has a physical body enters into the abyss, the Antakarana, which is the thread that connects the fourth and fifth human principles, is broken. Those inferior quaternaries which are separated from the spiritual triad become demons.
When a soul is very perverse, the Spirit abandons that soul. These people without Spirit are demons. Therefore, when the Spirit definitively abandons the body, the person passes through death, even though he may still be physically alive. Then, the name of this Spirit figures in the book of the deceased. Presently, there are many people who already do not have the Spirit (the Innermost). Whosoever loses the Innermost becomes a demon, and every demon belongs to the abyss." - The Aquarian Message