How the devil figure changed over time?

Answer 1

Satan entered post-Exilic Judaism as the 'adversary' but under the instructions of God, tasked to test the righteousness of the faithful. Jews continue to see Satan as the loyal assistant of God, rather than as the devil of Christianity. In Christianity, Satan evolved to become the evil opponent of God, seeking to cause the faithful to deviate from righteousness and to destroy God's kingdom. Satan continued to evolve throughout much of the Middle Ages, but the more the Church portrayed the devil as a repulsive being, usually either black or red and with horns and a tail, the more the common people made him a figure of fun in order to alleviate their fear of him. He is now an essential part of Christian belief, but if you did not read about Satan in books you believe to be true you would have no reason to think that he exists.

Answer 2

Satan has gone from being a title to being a real creature opposing the Church.