"Latter-day Saint theology is significantly different than the teachings of every other religion and philosophical religion concerning the origin and nature of evil," Brother Judd said. "Every spirit was innocent from the beginning, and evil had its beginning not in the Garden of Eden, but in the pre-mortal world."We had the ability to choose in the pre-earth life. We know this because we are now on the earth. We chose good and that earned us mortality. Those who chose evil joined Satan. They are denied mortality.
This is the origin of evil in L.D.S. (Mormon) theology.
The nature of evil is something we battle daily. For the most part, we share other religions' views on the nature of evil. However, recognizing evil for what it is, is not always easy. The trite cliché that we always have a choice between right and wrong doesn't always hold true. A series of wrong decisions can leave us in a situation where all our options are evil.
Evil comes cleverly and attractively packaged. When I took a Shakespeare class in college, our professor told us that in Elizabethan theater it was easy to know who would die, who would murder etc. The characters in question would always be dressed in a certain way, color etc. so you knew what was going to happen to them. I thought this was utterly ridiculous at the time. But, I don't think our modern entertainment is any different. Villains always look like villains. You can easily spot them before the plot develops.
But, it is never that simple for us in life. Outside the theater, villains don't always look like villains. Evil can be hard to spot. The devil wouldn't give himself away that easily.