I think its the 11th Doctor knocking. Both DT and RTD said it is not the master or anything you would think of, it is an emotional twist. 11 is life and death and he knocks on the door and forces the regeneration. Either that or RTD jumps the shark and its the Human Doctor and he kills 10. other than that its the valeyard played be Matt Smith Geffe71 17:51, December 31, 2009 (UTC)
He literally knocks four times. How could the 11th Doctor literally knock four times? They said the knocking will literally be heard, literal. A sin, knock, knock, knock, knock. How could the 11th Doctor knock? In order to do that, he would have to meet his 10th incarnation and then knock four times. But no, it's regeneration, or indeed death (they keep hinting the Doctor will die).
It needs to be someone who the Doctor can see and hear, someone who is literally there. Some people think it's Wilf. I personally keep picturing this sad scene where Wilf is dying, and to get the Doctor's attention, he knocks four times, and then dies. But it could by anyone, anything. But because the prophecy was very dark about the knocking, and the plot calls it the "deadly prophecy", it must be something really bad. How is the Doctor regeneration a deadly prophecy? And like I said, the Doctor needs to hear the knocking, and at least be in the room with whoever it is.
The four knocks may be linked to a character death, though. I mean, right before Abdelaide commited suicide, you hear a knock, knock, knock, knock. Delton Menace 20:28, December 31, 2009 (UTC)