Well we know that the nine are located in the Cis-Jovian planets, and we know that they presumably were human and then they made a pact with an alien force to survive the darkness. They seem to have some kind of connection with the Awoken, and it appears they were at war at some point. Thanks to some of the grimoire cards, we know the awoken "whisper to the stars" and they get a voice back, I think they whisper to the nine. They do have a hand in the events of destiny although their interference is mainly indirect (i.e. Skolas(more on this if requested) and sending Xur). Although the origins of them are unknown, it appears the darkness had an impact on them in some capacity, as Xur claims "So much light here, I suppose I feel pain", "I came to the light...perhaps...to understand the light", "Your traveler has a dark mirror" and the most implicating "The deep black is many things but never lonely". Although this doesn't mean that they are the enemy of humanity. I don't think the nine covet the strange coins, I think those are for Xur. As far as his appearance, I think that the transformation is necessary to survive in the territory of the nine, it is also implied that this is not Xurs only body. He says "For organic life to persist, it requires constant adaptation" and "Bodies come and go, but the cells remember, and if they forget, the Nine remember it for us". I think the pact with the alien force transformed them into this knowing their colony and life support would be destroyed, so they adapted their bodies to survive amongst the gas giants of the outer solar system.

Probably some cut storyline that got "Streamlined" and left many unanswered questions like the rest of the game...

What I find most interesting is the postmaster will occasionally say "Package for Xur. Which Xur?" Which leads me to believe every Xur we meet is possibly different. Or there's the one Xur who sells the good stuff and the one who likes to repeat his inventory for the fun of it. Or maybe "The Nine" refers to nine separate Xurs. They're also pretty much just matter pulled from the Universe, right? I can't remember exactly what he says but something about some of his cells are from Earth, I think. I also think he's said things that lead the player to believe The Nine are probably as old as the Universe itself. Theory? I don't think I have one other than maybe they're too weak to actually aid in battle and instead provide weaponry and armor of the highest tier. Maybe that's the only way they can play their part. Note: I've never read lore on Xur or The Nine, just pulling stuff from the game itself.

[quote]In the last year and a half, us Guardians have been met with a shady figure known as Xur, an Exotic weapon and armor seller.[/quote] Oh my god... A "shady" figure? This can only mean one thing! XÛR'S THE REAL SLIM SHADY!!!!!