Oh he's as real as the five fingers on your hand.... believe me... I served him for many years and was his prisoner.. until the One who could only set me FREE.. did....Jesus the Christ.... since then He has taught me about 'what' and 'who' had taken me prisoner...and he is real..
I agree with what Bob said here.....
Whether you want to believe in the EXISTENCE of a "personal Devil" or not is likely to become moot at some point in the future when you SEE him for who/what he is. You'll be chilled at how much he HATES you without having any interest in you whatsoever. But regardless, you will be "processed" by him and his agents.
Satan hates man and He hates God...He hates man because man was created in the image of God... and yes he hates 'immensely' without even having any interest in you whatsovever.. He especially hates the 'elect' of God.. he makes 'war' against those... One cannot imagine or begin to understand the 'immense hatred ' there is between satan and God.. and man.. until it is revealed to you by the Holy Ghost...
Personally I know of his intesne hatred and merciless activity.. even when I was a small child.. there was an instance when I was on family vacation.. I was probably 4-5 years old.. was fishing with my cousin on a dock..I did not know how to swim.. I was pushed from behind by 'something' into the water.. I was splashing and drowning.. by cousin jumped into the water to save me.. To them 'I fell in' into the water.. but I know there was something that physically pushed me into the water.. It was revealed to me after I asked Him about it...He said that the 'destroyer' wanted you gone....dead.. and yes even as a young child.. why? I don't really understand... but Jesus wouldn't let the destroyer take my life... Jesus was again standing there holding back the gates of hell as He has the 'keys' to them...as they were ready to swallow me up.. He used my cousin as an instrument to pull me out of the water.. and the first thing I did after He saved me in 1994.. I wrote my cousin a letter and 'thanked' him for being there to help me out of the water.. that was almost 40 years ago.. I remember that as clear as crystal.... I can still feel that 'push' from behind and falling into the cold water.. my cousin pulling me out and running me back to the cabin.. I thank God thru the Lord Jesus Christ that He was there to hold back the 'destroyer' , satan, from taking a young boys life... I understand today that He did that.. so that on Feb3 1994, a date He knew some 40 years later.. He would reveal Himself to me.. bringing me to repentance and Salvation.. His goodness and mercy.... the revelation of it.. bringing me to my knees... being Born Again by the will of God...
If you are 'His'.. that is Jesus the Christ's.. you will encounter your spiritual adversary.. there is no way around it.. he knows who you are and you 'will' know who he is and what he is about.. thru the Power of the Spirit and the Wisdom and knowledge of Jesus Christ..
Many appear Righteous and Just because they say 'yes' to Jesus Christ , yet they don't do His Will.
Verily I say unto thee, the tax collectors and the prostitutes go into the Kingdom of Heaven before you do.
The LORD hath appeared of old unto me, saying. YEA, I have loved thee with an everlasting love; therefore with LOVINGKINDESS have I DRAWN THEE.