One of those things, I suppose, for certain people, a specific actor becomes the definitive one for a particular role. for me, David Suchet will always be the Poirot, if only because he got the fussy mannerisms right, as well as the wholly intellectual method of solving mysteries. Branagh is too physically active and Ustinov too large a man.
Then again, it can hinge on a number of factors, I suppose. generation being one - Sean Connery is my Bond, if only because Roger Moore was The Saint! (Derren Nesbitt once told me that he was standing next to Moore on set, and Moore said to him "You know, Derren, I'm very tall, very suave and have a good speaking voice. I'm just afraid that one day they'll realise I can't fucking act!").
By the same token, Jeremy Brett will always be the definitive Sherlock Holmes, despite Benidorm Cummerbunds' best efforts!
Funnily enough, I don't have such a fixed opinion about Dracula - Lugosi, Lee and even Gary Oldman played the part in ways that suited the (very different) styles of the films they played him in.
On the other hand, I very much doubt that Emily blunt will ever overshadow Julie Andrews as Mary Poppins (Emma Watson might have, if only because Ms Poppins and Ms Granger have so much in common -ie bossiness).
The Christopher Reeve/Henry Cavill debate around Superman will run and run, I think. As to the Batman, my personal preference is for Ben Afflecks' grizzled, tech-savvy, always one step ahead iteration.
For the record, my favourite Doctors (thus far), have been Hartnell, Pertwee, McCoy and Capaldi. All the others have been to young, too nice, or both!
I do wonder, though, if any work has been done on the whys and wherefores of how some actors become so associated with specific roles, while others don't? Sir Patrick Stewart, for instance, played Captain Jean-Luc Picard - the lead in a highly-regarded (almost revered) franchise, and yet has gone on to play Professor Xavier, Scrooge and Captain Ahab without anyone batting an eyelid, while other actors have taken the role of Xavier without anyone kicking off (except Deadpool). On the other hand, there is no doubt that, for now at least, Robrt Downey Jr owns Tony Stark/Iron Man.
Probably something to do with zeitgeist, or quantum. Quantum zeitgeist? Schrodingers' Cast? Don't get me started!
