Christian 20/80 Atheist, What if in the OT God was both good and evil?

God was never evil, but you can’t just look at the OT and see God clearly.

John 1:18 (AMPC) No man has ever seen God at any time; the only unique Son, or the only begotten God, Who is in the bosom [in the intimate presence] of the Father, He has declared Him [He has revealed Him and brought Him out where He can be seen; He has interpreted Him and He has made Him known].

Hebrews 1:1 (NIV) In the past God spoke to our ancestors through the prophets at many times and in various ways, 2 but in these last days he has spoken to us by his Son, whom he appointed heir of all things, and through whom also he made the universe. 3 The Son is the radiance of God’s glory and the exact representation of his being, sustaining all things by his powerful word. After he had provided purification for sins, he sat down at the right hand of the Majesty in heaven.

 2 Corinthians 3:14 (NIV) But their minds were made dull, for to this day the same veil remains when the old covenant is read. It has not been removed, because only in Christ is it taken away. 15 Even to this day when Moses is read, a veil covers their hearts. 16 But whenever anyone turns to the Lord, the veil is taken away. 17 Now the Lord is the Spirit, and where the Spirit of the Lord is, there is freedom.

He wasn't.  One can only be a real God if he is good.  But good fathers sometimes have to use tough love.

You are subscribing to an ancient heresy last promoted by the late, European Cathars. 

The devil was created by God as an angel named Lucifer.  Lucifer rebelled against God and thus God, in His Justice, sentenced him to eternal damnation.  God is all-powerful and thus Lucifer and the other demons could not even exist without God sustaining them in existence.  God is omnibenevolent.