Once upon a time there was an angel named Lucifer. He was a very arrogant angel, and he was very proud. That's very bad, since pride is one of the seven deadly sins. Anyway, Lucifer decided that he wanted to take over Heaven, because he thought he was better than everyone. Even GOD.
So, Lucifer was mad because God had a bigger pool and a bigger house than he did. Because he lived in the angel apartment complex, and it was cool, but not cool enough for Lucifer. So he decided he wanted to steal God's mansion.
He snuck in one night into God's hilltop mansion. He made his way slowly to God's room, and then tackled him. But God was stronger, because you know, he's God. So they were all fighting and wrestling and whatnot, until eventually they were standing over the cloud cliff behind God's mansion. And since God was stronger, he threw Lucifer off the cliff, and Lucifer fell down to Earth. And since Heaven was so high up, Lucifer's wings burnt up and he got tan, so he wasn't white and shiny anymore. Anyways, after he landed on Earth, he bought this place and named it Hell. And he called all his bad fallen angel buddies and formed a gang. They called that gang "The Demons". Lucifer's gang name was "Satan".
That's basically Lucifer's story. For now.