What iconic characters can you not imagine being played by anyone else?

For me, definitely Patrick Stewart as Professor X. Sure, he looks exactly like him but, can you imagine if the casting department gave the role to someone else? It's just ridiculous. Other examples are Jim Carey in "The Mask", and "Ace Ventura: Pet Detective." Kevin Spacey in "American Beauty"(stupid movie but, Kevin Spacey IS Lester Burnham, there's no other explanation for his freaky good acting in that. Another one that is not a movie but, You just can't possibly fathom anyone in the role as Walter White besides from the great Bryan Cranston. Then of course there's also Robin Williams who brought so much beautiful life to each of his characters that the idea of anyone else in his roles is offensive, his best being the Genie in "Aladdin", Mr. Keating in "Dead Poet's Society and of course Mrs. Doubtfire.

Can you see those characters differently at all? I can't. It's like those roles were written specifically for them only.