well, it’s not as if Satan was created by God as a contrasting force. Satan/Lucifer/the Devil is an angel that wanted the same power as God, but was cast out of heaven.
Evil is anything contrary to or against God. Evil exists because people choose to do it. God lets us freely choose to love and follow him rather than create us as robots because it is more authentic, it’s a true love. Evil is the result of choice, bad choice.