No One Else Could Have Played That Role

I’d say John Malkovich in Being John Malkovich.

Casting someone else would just be weird.

Cates was born in 1963. Filming started in 1975. That's a young princess.
Leigh was born in 1962, so 13-14 for Leigh's Leia. Maybe they're on a field trip?

Penn was born in 1960. This is a plausible age for young Luke.
Romanus was born in 1956. A bit young for smuggler? 20-ish?
Walston was born in 1914, which does not matter since C-3PO is a droid and he's awesome.
Whitaker was born 1961. Would he have grown into his voice yet?
Backer was born in 1956, so sure, cut off his f***ing arms and legs and stuff him into R2D2 (you monster!)
Cage was born in 1964. Nah. He would not be tall enough yet. A whelp.
Schiavelli was born in 1948, so yeah, he fits.
Stoltz. Why you gotta do my man dirty like that? Greedo? That some kinda awful.

Yeah, I was going to put a caveat at the end saying most of the cast of Ridgemont High would've been a bit too young to be in Star Wars (most of the ones playing teenagers hadn't even appeared on film when Star Wars came out) - but I figured everyone would understand that for a fun / speculation post of swapping casts from one movie to another.

P.S. I had Ray Walston as Obi Wan (not a droid)... could you see him mentoring Luke just like "Mr. Hand" mentored "Spicoli"?

It was an inspired gag. I like the idea of cast-swapping, some weird cosmic swingers party where the toys from one movie substitute into another. Forgive my literality. My brain was having too much fun with it. We shall assume temporal relativity such that they shall be the age they were in the film of origin.

True. I think at least one person on this thread has said that they couldn’t imagine anybody but Harrison Ford playing Indiana Jones. I agree, but that’s mainly because Harrison Ford was the one who got the role. Tom Selleck, among others, was offered the role first and turned it down. If he had accepted and turned in a memorable performance as Indy, then people today would be saying they couldn’t imagine anybody but him in that role.
I could be wrong about this, but I think that one reason why Ford wasn’t offered the Indy role from the jump was because Lucas and Spielberg were worried that he would remind people too much of Han Solo. One of the remarkable things about Ford’s portrayal of Indy is that whenever I see an Indiana Jones movie, I think of him only as Indy and not at all as Solo.

I don't think we can get past the purely human element of familiarity in appearance, voice and mannerisms. It's basic to us as humans to recognize people; we do that all the time. Tom Cruise as Luke, John Wayne as Han Solo....doesn't work if we'd seen the previous versions of those characters. The more engaging the character is, the less likely it would work.

Good points. I love reading about the making of movies, in part because it’s fun to see who was offered and turned down iconic roles or was even cast and played the part for a time before leaving the production. You probably know that Stuart Townsend was originally cast as Aragorn in The Lord of the Rings. I don’t know who Townsend is, but I can’t imagine anyone but Viggo Mortensen in that role, which is remarkable because I’d seen his earlier movies (i.e. Young Gun II, Crimson Tide, G.I. Jane, etc.), and NONE of those roles would have led me to believe that he could have been perfect as Aragorn, and yet he was.

Totally agree with that. But I think some of us, at least me, are slicing it differently. That is to say I image what if Mark Hamil had never played Luke so we don't have that image in our heads, with that in mind I can see Tom Cruise being a great Luke. Like all things in life we often are thinking along similar yet different lines.

Never heard of it. The name Lestat sounds familiar though. I think there was a vampire named Lestat in Interview with the Vampire.

Anthony Perkins as Norman Bates...

I was thinking about Anthony Perkins as Norman Bates and I can't see any actor working at that time who would've been able to elevate Psycho to greatness like Perkins did.

He's good as Mr K in The Trial too. His fear is palpable. I thought he did a very good job there.

I doubt anyone else could have been Charles Foster Kane in Citizen Kane because Orson Welles wouldn't let anyone else take the role. It was his baby and no one could mess with it. This is unconfirmed supposition and not researched knowledge.

He shall cast no role himself he holds.
--Paul Mason (probably)

He shall cast no role himself he holds.
--Paul Mason (probably)

Anthony Perkins as Norman Bates
Adam West as TV Batman