Legendary Background

Most, if not all, legendary Pokémon have their own background story, which explains as to what they are, how they've come into being, and so forth.

One example of this would be Deoxys. Hopefully, I'm not wrong, but apparently, this Pokémon was once said to be some small creature which landed on Earth from outer-space; thanks to the atmosphere, it eventually began to grow its body, leading to birth of Deoxys. The gem on its stomach is also said to be its brain; it generates all its power with help from it.

So, of all stories we have heard before relating to legendaries, which would we say is our most favorite, and why? What part of it are we most interested in? Which myth would be our least favorite, and why do we find ourselves disliking it? If we were to create a background for any new or existing legendary, how would it go?

Something about Rayquaza having lived in the ozone layer for hundreds of millions of years has always intrigued me, and that's part of the reason why it's one of my favorite legendary Pokemon. I mean, that number's probably greatly exaggerated, even by in-game standards, but if Rayquaza were to descend from the skies just once every couple of years, that would still be a remarkable sight, and one I would want to be there to see in person.