Now that you've got me started
I'll add a few more examples of this phenomenon:
Scarlett O'Hara. Now, I worship at the shrine of Vivien Leigh and I think she didn't just act Scarlett, she EMBODIED Scarlett. There are so many things I love about that performance, from Vivien's almost manic, brittle way of talking, to the fact that she singlehandedly, against all the advice from director Victor Fleming and costar Clark Gable, made Scarlett a complex character, worthy of our respect and affection. But that being said, the very first line of Margaret Mitchell's novel is "Scarlett O'Hara was not beautiful." It's clear that Scarlett is very pretty, and quite the flirt. But Vivien Leigh happened to be literally among the short list of most beautiful women, EVER. Of course I got the GWTW dvd boxset which had some truly horrifying screen tests from the likes of Lana Turner and Katharine Hepburn, so I should thank my lucky stars that Vivien was ultimately cast
An opposite phenomenon happened with Sense and Sensibility. Elinor and Marianne are supposed to be close in age, but next to the luminous Kate Winslet, Emma Thompson looked like a plain soccer mom. Thompson CAN look very beautiful, but in this movie the huge age difference between the two sisters really would have horrified Jane Austen, I should think.
A movie that I think got things exactly right was "The Age of Innocence." Daniel Day Lewis was just about right as Newland -- mildly handsome but not really dashing. Michelle Pfeiffer was glamorous and appealing but had the kind of aged, world-weary look that reminded viewers that Ellen was running away from an abusive marriage. And Winona Ryder was perfect as May: young and innocent looking, but with enough steeliness to be scary. That scene when she tells Newland she's pregnant -- crying and gloating at the same time -- always gives me the chills.
On the opposite end of the spectrum, a movie that got things totally WRONG was The Great Gatsby. F. Scott Fitzgerald is pretty explicit about Gatsby -- he's sort of phony looking, with an eager smile and "beautiful shirts", but in the end he's just a thirty-something "roughneck." In other words, not Robert Redford. And Mia Farrow bugged me to no end as Daisy, especially her pipsqueak rather whiny voice. Hello! Daisy's voice is supposed to be so alluring even Nick is totally transfixed by it. It's the most important part of Daisy. Did the producers and director even read the book?