I would probably say Troughton. While Hartnell originates the character, it seems to be Troughton that defines how the later Doctors do things. It might be that the writers decides that this was how th Doctor was, or maybe it was that the later actors who played the Doctor were inspired more by Troughton than Hartnell.
The main one that is different is of course Tom Baker, who from what I can tell, was being Tom Baker. The writers were still were probably still doing the Doctor (as based on Troughton), but Baker does what he does. And it wonderfully sticks to the Doctor until the present.
Today, the writers write a script for the Doctor. Then you get an actor who plays the Doctor. At that point the personality of the new actor changes the way it works in little ways so it becomes them as the Doctor. The basic Doctor doesn't change.
Throw 1960s Patrick Troughton into a modern episode of Doctor Who and while you'd get a different preformance, you would still get The Doctor. You put William Hartnell in there and I'm not sure what you'd get. Probably the Doctor, maybe.
The main one that is different is of course Tom Baker, who from what I can tell, was being Tom Baker. The writers were still were probably still doing the Doctor (as based on Troughton), but Baker does what he does. And it wonderfully sticks to the Doctor until the present.
Today, the writers write a script for the Doctor. Then you get an actor who plays the Doctor. At that point the personality of the new actor changes the way it works in little ways so it becomes them as the Doctor. The basic Doctor doesn't change.
Throw 1960s Patrick Troughton into a modern episode of Doctor Who and while you'd get a different preformance, you would still get The Doctor. You put William Hartnell in there and I'm not sure what you'd get. Probably the Doctor, maybe.