Brent Spiner is always Data to me, although he does very well in every other role I’ve seen him in.
Anthony Perkins is always Norman Bates, and creeps me out no matter who he plays.
Adam West
I think one reason Gandolfini did not want to do any more Sopranos was he did not want to play Tony type roles forever. He hasn’t had much success since the Sopranos ended.
I can’t watch House.
He’ll always be Baldrick to me!
I think you mean the Prince Regent.
Baldrick hosts (hosted? not sure if it’s still being made) an archaeology show about old Roman forts and suchlike in people’s back fields.
I think you mean the Prince Regent. 
Reubens was pretty good in the minor role he had in Mystery Men (The Spleen — “Silent but Deadly!”)
Tim Curry as Dr. Frank-N-Furter. He always give off kind of a creepy vibe anyway, but regardless of what he’s on I always see the fishnet stocking and bustier - even in Kinsey where he played a prudish professor.
George C. Scott is often cited, but in a slightly different way than the others mentioned. His performance in Patton overwhelmed any memory most people might have had of the real General Patton, such that hardly anyone today could tell you what the real general looked like, but say “Patton” and you’ll automatically think of Scott.
However, that doesn’t mean Scott wasn’t memorable in other roles as well – he certainly was, in films like Dr. Strangelove.
Nimoy as Spock was the first person who came to mind.
Not Shatner so much because of his work in other roles.
Michael Richards as Kramer.
He was in UHF and Problem Child but he pretty much played Kramer-ish roles in those too. So now he’s Kramer…or, if you prefer, Racist Kramer.
I saw Breakfast at Tiffany’s for the first time a few months back, and the whole time I kept expecting George Peppard to turn to Audrey Hepburn and say, “I love it when a plan comes together”.
This is going back a bit, but … Larry Linville and Gary Burghoff (“Frank Burns” and “Radar O’Reilly” from MASH**) and Richard Sanders and Frank Bonner (“Les Nessman” and “Herb Tarlek”, WKRP In Cincinnati). I guess that’s the danger of creating a memorable character - you’re always that character.
Agree, that’s the first person I thought of. His character in *True Romance *could have easily been young Tony Soprano.
Well… except that he died.
…Richard Belzer as John Munch.
Paul Reubens was also great in the Buffy the Vampire Slayer movie. His last scene is priceless.
As for typecasting, I didn’t watch NCIS for the first few seasons because to me, Mark Harmon should always be a doctor, preferably in nicely tailored scrubs. But now I would have a hard time picturing him as anything other than a member of federal law enforcement.
The benefactor who began his career, though, Jack Webb, could never ever be anything but Joe Friday.
I like Woody Allen movies – except for that nervous redhaired guy that’s always in 'em.
You should see a film he did a few years ago called “Recovery,” about a man who receives a serious brain injury in a car crash and how it changes his entire family. It’s a really brilliant performance, completely unlike The Doctor (not that he wasn’t brilliant as The Doctor, but you know what I mean.) I think it might be on DVD? Not sure about that. Sarah Parish, a frequent co-star of his, plays his wife.
I know what Patton looked like. He had very narrow, piercing eyes. Didn’t look much like George C. Scott but was definitely equally striking in appearance.
I can’t believe no one else has said Kelsey Grammer as Frasier.