Everytime I see that "old man" in the secret ending pictures, I think "boy, you shore is UGLY!!" AHAHAHA! Yea, dumb I know.
One of the maintainers of KH Insider mentioned that his outfit is exactly the same as "Ansem's". Uh-huh. Coincidence?
I haven't the foggiest. I'm thinking that the "Old Man" was "Renoath" or "Another" or whatever, and his power was somehow like that of a god, so when he lost his Heart, he became "Xehanort" and the being by his side was his "Heartless". During the experiments, he may have regained his memory somehow, and that would explain why the outfits were identical. Only thing is that, no one knows that he regained his memories because he had PLANZ involving both himself ("Ansem") and his Nobody "Xemnas". Or, rather, they had the same plans. Or something. Bleh, I don't know. This doesn't even make any sense.
I also think that ugly old man is Xehanort's father. The "being" beside him is his son, or replica of his son(yea right), and he is defeated and has no memories of the fight. The father disappears somewhere, leaving his son under the care of Ansem the Wise, and his son only remembers being "Xehanort", and despite the loss of memories, he knows that he must fight his father's battles or something like that.
Bleagh. Course the Old Man could also be "Renoath", who lost his Heart and became "Xehanort", but because he was so damned powerful, he really only lost half his Heart. Then Xehanort lost the remainder and became "Ansem/Xemnas".
Whatever. This is one of those things that will be blabbed out for a long time, I'm sure.
All I know is that Old Man is UGLY. Heh.