satan
A figure created by the Jewish, Christian, and Islamic religions (and their sects) to represent 'evil,' respresenting such ideas as selfishness, hubris, hedonism, free thought, and malice.

Every person has a bit of Satan in them. While these religion represent the death of Satan, it would only be more natural to balance the idea within you, rather than reject one totally.
A real religion would worship God and Satan together as two different aspects of the same whole.