There are those who don’t believe that Satan exists, and in many cases they are the same persons who don’t believe that God exists.
But the scriptural evidence supports the existence of both. The whole of the Old Testament assumes the existence of Satan as much as it assumes the existence of God. The book of Genesis is built upon the reality of Satan working through the serpent to cause the downfall of man through sin. Satan is mentioned many times in the Hebrew text and in the Quran.