The defining, overriding, central issue to Dr Who, since RTD relaunched it in 2005, is The Time War.
The Doctor shifted from "Wandering vagabond with a mysterious past" to "Last survivor of his race, who killed (nearly) all of them, and (nearly) all of their greatest enemies".
It gave him pathos, and drama, and interesting psychological issues to deal with.
And then, over the next eight years, it became clear that it also tied him inextricably to them. Everything else paled before the fact that he was The Loneliest, The Oldest, The Lastest.
How do you deal with that? What do you have to do to a character to have them move on from that? How do you cut the knot that entangles them and free them to take on a very different approach?
Steven Moffat found his blade to slice through that. His answer: "It never happened, and this is how."
Ecclestone was the man who ran from the war - through refugees and unexploded bombs, war criminals and survivors. Until he died.
Tennant was the man who ran towards the endangered, striving to make a difference, to make up for the Wrong he'd done - celebrating the amazingness of the ordinary lives he encountered, until it rang completely hollow through repetition. And then he died.
Smith was the man who ran from himself. Who forgot what he could, hid from his past, his enemies, his friends, and his future. Who spent hundreds of years doing who-knows-what so he wouldn't have to deal with any of it, least of all himself.
Now he's free from his past. Soon he'll face his future. And he'll die.
I wonder how Capaldi will run.
Original post on Dreamwidth - there are comments there.