The problem of evil

Here is an excellent Q&A regarding the age-old question of how evil can exist if there is a good God. The response includes this accurate definition of evil:

Evil is not a thing in and of itself. It is the absence of a thing, namely good. Good is a thing which does exist in and of itself. It exists first and foremost in God who is His own supreme, eternal, and infinite Goodness. It is impossible that evil could exist in God. Evil is really a nonentity or a privation like darkness. Darkness is not a thing either but is really just the result when light is taken away. So good and evil do not have equal standing. Good exists in itself. Evil is a kind of parasite which exists only in some relation to things that are good.

For Lord of the Rings fans, this very point is one of the main ways that, although as a work of science fiction it doesn't directly reference Christianity, the underlying worldview in J.R.R. Tolkien's Middle Earth is fundamentally Christian. Looking at the characters, many of the "bad" ones are simply evil derivations of other "good" characters. Orcs came about from an original corruption of elves; Gollum, due to his self-obsessed hording of the Ring, is a shadow of his former person as the happy-go-lucky Smeagol. And the list goes on.

Back to real life, we can rest assured that only God has the power to create and that what He created is good; Satan has merely been given the power to corrupt what is already there. And that is another reason why we can be confident that, though evil may sometimes seem to have its way here on earth, in the end the ultimate victory will be reserved for God alone.