Thought I'd post this in here for the hell of it:
We can't forget the all too important phrase, "It all began with Birth by Sleep". I've really been trying to take this from a logical point of view. What began with Birth by Sleep? Obviously the events of the Kingdom Hearts series. And so what then, would be the original cause that spurred on these events? Xehanort, clearly (at the moment). It must have been his arrival, or his creation. So, then, Xehanort was born by "Sleep"? Maybe. This quote certainly suggests it:
QUOTE
The wall of light and darkness exceeded each other, creating the original me, and Terra waited for me impatiently
So then now we need to ascertain as to what exactly is meant by "Sleep". Since the first time we saw the secret ending, people have suggested that Sleep refers to Sora's year of sleep or Riku's sleep in the prologue of CoM (among other theories). Neither make sense since it all began with Birth by Sleep, meaning that whatever this Sleep was, it was in the past and preceded all other events. However, those two might work in concept. Sleep might refer to literal sleep, as is the case with Sora, or a metaphorical sleep, much like with Riku. While I'm not ruling it out, I'll put aside the literal meaning of Sleep for the moment, mainly because there's a connection for Riku's type of sleep. "The wall of light and darkness". This should sound familiar:
QUOTE
You've been sleeping here between light and dark... Here, blanketed by darkness, sleep is safety. Sleep is eternal.
Go here if you haven't realized yet:
http://www.youtube.com/watch?v=i90a5hpA-a4...feature=related
Now, I'm not implicating that Riku's specific event has anything to do with Birth by Sleep, but it could be that Birth by Sleep occurred in a similar manner. This would be for Master Xehanort. And that's also where I believe the "Another" and "No Heart" comes in. People say Another might suggest that the Xehanort we know is Another (Master) Xehanort, which would make no sense considering the name, which serves as an anagram for Another, would suggest that Master Xehanort is Another since he is the one who originally had the name. How it all plays out, no clue. But Master Xehanort's creation must have had Terra involved, since he was "waiting impatiently". However, I don't know if Terra was directly involved or if he simply knew about it because I have my hunches that the creation might be connected to Ven, DS, or both. Ven because he knows Xehanort, but has forgotten about him. Also, the fact that "Ven" is an alias has me suspicious. People brush it off as his true name simple being Ventus, but I can't help but feel that it would be obvious. Nomura is refraining from saying the true name for a reason, and Ven is an ALIAS, not a nickname. I think the true name might have something to do with Xehanort. Lastly, there's the quote of Master Xehanort that sounds similar to DiZ talking to Riku:
MX: It seems you have lost something. However unless what you have lost is put back into your hands, it will be an eternal lost. Once you obtain it, grip it and understand the truth.
DiZ: Sleep is
eternal. It is a door to the
truth. Take it, and your sleep ends. Take it, and take your first step towards the truth.
This statement by Master Xehanort is also extremely similar to the one given to Sora by Marluxia. It leads me to believe that Castle Oblivion plays a role as well. This is not the sole reason, though. Nomura said Castle Oblivion was around before the Organization and that they simply found it. My bet would be that Master Xehanort created it, as there's no way he can leave this up in the air.
While I'm at it, I might as well post this too, which is evidence for Xehanort possessing Terra (or something along those lines):
The ONLY thing that was done to that picture of Xehanort was recoloring of his eyes, skin, and hair. Their facial similarities, in my opinion, are beyond coincidence.