The Changes in Tony's Identity in "The Shining" (from the page to the screen).
Danny from the movie version of "The Shining"
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Tony is very different from page to screen.
I recently went on kind of a Stephen King kick, after a cousin of mine was describing something that he had read about what someone thought that they had seen in the undercurrent of The Shining. I went into the book, not looking for it specifically, but keeping myself open to see what he said that someone had said that they had seen in there. I didn't see any of it, but what I didn't notice (and something that did make me wonder) was the change of the character of Tony between the book and the Stanley Krubrick version of the story.
Warning: There will be spoilers beyond this point for both the book and the movie.
In the book, Stephen King doesn't come right and tell us who Tony actually is, even while Wendy (Danny's mother) says that she is fully aware of Tony's identity. But by the end of the book, a hint is given to who he actually is, when Danny's full name is stated. It is eluded to (through the admission of Danny's middle name of "Anthony") that Tony is actually Danny a few years in the future, and that he has been giving Danny information about different things (like where to find something that his parents thought that they had lost, or what to look out about when it comes to the Overlook Hotel). What seems to be implied by this is that since Tony (being Danny in the future) already knows what is going to happen to Danny during his family's time at the Overlook Hotel, Tony is trying to help him to survive so that the hotel can't keep his spirit there forever.
But when happens when the story moves from one medium to the other (in this case, from the written word to the silver screen), Tony is changed ... and it is a change that is not necessarily needed, or one that is kept going throughout the parts of the film that seem like one that Tony would be needed the most (per the way the writers of the screenplay decided to present him). Instead of being Danny from a few years in the future, Tony is presented as an alternate personality of Danny's. Yes, it is true that the term "imaginary friend" does make its way from book to screen, but in neither instance is that term completely believed by anyone who is trying to assert that it is what is really going on.
When things really start getting bad for Danny, and it looks like Jack is getting to the point where he's about to snap and start hurting his family, Tony takes over (and "Danny isn't here anymore"). It gives the impression that through the trauma of what is going on, and the fear of what might happen to himself and his mother, Danny retreats inside of his own mind and lets an alternate personality take over so that his mind (as Danny) can continue to function without the scars and damage that he is probably sure are about to come upon him. This could be something that makes sense within the story itself; after all, the stress that was upon him from what the hotel kept throwing at him, and the crazy things that his father was doing around that same time would probably make anyone want to retreat within themselves to help protect their own mind.
The part where this starts to break down, however, is that during the point where Tony as the alternate (and protecting) personality would be most needed, he suddenly disappears. When the family is right on the cusp of something truly horrible happening, Tony takes over and Danny hides inside himself and refuses to come out. But when the dam breaks (so to speak), Tony suddenly disappears and leaves Danny to fight on his own. It was Tony that said that Danny was gone and that he didn't want to talk in the hours before Jack succumbed to the hotel; but it was Danny that was in control (and Tony that had left) when Jack was chasing his son through the hotel's hedge maze with the intent on killing him. This change does not make sense for what Kubrick and his team were trying to put forward about who Tony was, and his relationship with Danny. If Tony really was the alternate part of Danny's mind that was there as a protector, who would keep all of the horrible parts of their lives out of Danny's memory, it makes little sense that he would suddenly disappear when Danny needed him most. If this is not what Kubrick and his team wanted Tony to be, perhaps they should not have presented Tony as this up until the very point when he would have been needed the most.