The battle between right and wrong, moral and immoral, virtuous and vile is as old as recorded history. In the Garden of Eden God placed the Tree of the Knowledge of Good and Evil and directed man not to eat of it, adding that death would occur if man ate of that tree (Genesis 2:17). Man was given a choice whether to obey or disobey. Today, the conflict still rages.
At times, good and evil can reside in the same person. Robert Louis Stevenson wrote about this in his famous book, The Strange Case of Dr. Jekyll and Mr. Hyde, the story of a man with a multiple personality disorder.