I was recently asked about the whole God and Satan thing. As I recall, Lucifer was mostly pissed that God held humans in higher regard than angels even though they had no super powers.
And then God said humans were superior even without super powers because they had free will, then Lucifer said "fuck you" (demonstrating his lack of free will in some way) and got a bunch of his buddies to start a war with the other angels, then God said "fuck you too" and banished him to another dimension.
Then God decided to make the best of the situation by using Lucifer to weed out the humans he doesn't like in some selection process so they didn't stink up Heaven with their sex pheromones.
Now aren't you glad you asked?