Satan the Devil is the personification of the lust within all men and women which tempts them to sin.
James 1:14-15 But every man is tempted, when he is drawn away of his own lust, and enticed. 15 Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death.
All evil comes from within man.
Mark 7:21-23 For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, 22 Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness: 23 All these evil things come from within, and defile the man.
These are called the works of the flesh
Galatians 5:19-21 Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, 20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, 21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.
The lusts are categorised
1 John 2:16-17 For all that is in the world, the lust of the flesh, and the lust of the eyes, and the pride of life, is not of the Father, but is of the world. 17 And the world passeth away, and the lust thereof: but he that doeth the will of God abideth for ever.
Evil arising from the lust within ourselves we can counter.
James 4:7 Submit yourselves therefore to God. Resist the devil, and he will flee from you.
Evil arising from the lust in others we cannot counter.
Revelation 2:10 Fear none of those things which thou shalt suffer: behold, the devil shall cast some of you into prison, that ye may be tried; and ye shall have tribulation ten days: be thou faithful unto death, and I will give thee a crown of life.
Devils (demons) likewise are not supernatural entities they are the personification of mental illnesses. Thus, we are responsible for our own sins and judged accordingly.
Do you believe in a Devil? (click on the title)
Demons - A Biblical and Historical Study (click on the title)
I hope you find this helpful.