Who was behind the plot to lock the Doctor inside the Pandorica and blow up the TARDIS, causing the end of time and space? The TARDIS is not an easy thing to blow up. It can survive a lot of things, and it would take something serious to blow it up ... or someone with an intimate knowledge of it, which correlates with the fact that someone was controlling it and keeping River, who knows how to operate it, from doing anything.

My current theory is some sort of evil version of the Doctor, something akin to the Dream Lord we saw. Perhaps the Dream Lord episode was to establish that such a thing is possible, reinforced by the Doctor seeing it again in his reflection.

After all, who else would make such a perfect enemy? Who else could unite all of the Doctor's foes and trick them into allowing the destruction of all reality?

Alternate theories include some sort of other Time Lord, but the Doctor has stated before that if another Time Lord existed, he would be able to feel it, so ... (we would have to assume that this rule wouldn't apply to an evil version of himself, I suppose).

Any guesses?