Lucifer
Gabriel had two younger brothers and a younger sister. Michael, Raphael, Uriel, Gabriel, Jophiel, Selaphiel, and Zadakiel were the first of the Cherubim, and the most powerful. But they were still young, and still training. Jophiel and Zadakiel both trained as warriors with Michael and Raphael. Selaphiel was mentored by Uriel. Gabriel, however, wasn't like his siblings. He had begun training with Michael and found himself to be very good with a blade. He was clever, also, and sometimes beat Uriel with his strategies. Combining these skills allowed Gabriel to defeat Raphael almost every time they sparred. If it weren't for Michael's pure swordsmanship, he would have been defeated by Gabriel often as well. The younger ones were no match for him at all.
Then one day, their Father created Lucifer.
Lucifer was a lower level Cherub, but he was the most beautiful of them. None would argue it. They all loved Lucifer, their baby brother. Michael himself taught him to fight. But Lucifer adored Gabriel as much as Gabriel adored Michael. And Gabriel loved Lucifer just as much.
"Gabriel, where is our Father?" Lucifer would ask, and Gabriel would be reminded of himself. He would smile fondly and answer,
"Father is creating our younger siblings. He is also creating a new thing he calls Earth." Lucifer would look at Gabriel with wide, curious eyes.
"Can we visit Earth, Gabriel?" Gabriel would chuckle. Was he really like this not so long ago?
"Not yet, Little Brother. Father is not finished."
Lucifer once questioned Gabriel about his wings.
"Brother, why are your wings not gold?"
"I don't know, Lucifer. But it does not matter."
"I want wings like yours, Gabriel. Does Father not think I'm special?" Gabriel was a little shocked at how much Lucifer was like him.
"Of course he does. You are special to all of us, Lucifer." Lucifer grinned up at him.
"I want to be like you, Gabriel." Gabriel smiled down at his little brother, but he couldn't see why. He was so different than the others. He didn't… he didn't belong with his brothers and sisters. What had his Father planned for Gabriel? Why was he so different?
So, just to destroy any who take Supernatural to heart, LUCIFER IS NOT AN ARCHANGEL. There are in fact seven archangels, and Lucifer is not one of them. The only ones actually stated by name are Michael and Gabriel. Raphael is a given, and Uriel is almost always one of them (even though he was basically disowned by the Vatican...). The other three vary.
This fic is mostly from my mind, but some of it is from actual mythologies and lore, and some will be from the show.
So there's that. Please keep reading!