In early depictions the devil was a clown like figure who couldn't really get shyt right and always got fooled by the big G and his son. Kind of like a Scooby Doo villain.
The Catholic Church started to build up the idea of a truly powerful and devious Satan as almost like an extortion tactic - they created a boogey man so they could ask for more money to protect Catholics from him
But if you really wanna go down the rabbit hole, the views of the Cathar heretics in Medieval times elieved in 2 powers of equal or near equivalent power, one evil and one good. This world we live in is owned by the evil one and our souls are trapped here in these mortal bodies which are really cages. We just tryna get home to heaven where we all angels
Catharism - Wikipedia