Clint Eastwood has done a lot more with his career, but in a sense he’ll always be both The Man With No Name and Dirty Harry.
This is what I was coming in to say. And I think the two roles effectively bracketed his career, too.
Raymond Burr as Perry Mason and Ironside.
Another TV one: Jack Klugman, as Oscar Madison on The Odd Couple, and the title character on Quincy.
Levar Burton as Kunta Kinte and Geordi LaForge. (John Amos, who he tag-teamed as Kunta, is also strongly identified as James Evans on Good Times and as Mr. McDowell in Coming to America.)
It’s hard to pick which of his main three roles Marlon Brando is associated with:
Stanley Kowalski
Terry Malloy
Vito Corleone
There are even others he may affect different viewers with.
For me, Paul Newman is either Butch Cassidy or Cool Hand Luke.
Vivien Leigh is Scarlett O’Hara and/or Blanche DuBois
Patrick Stewart is Captain Picard and Professor X.
Dirk Benedict: Starbuck & Face
Dwight Shultz: Murdock & Barclay
Ricardo Montalban: Roarke & Khan
Michael J. Fox: Keaton, McFly, Flaherty
And the cutie from Reading Rainbow. He is solidly in my mind as those three people.
Michael Chiklis is The Commish & Vic Mackey. And two starring roles don’t come much more different than those.
His co-star Ian McKellan is Magneto and Gandalf. (I don’t know whether it’s true but he says he was offered the role of Dumbledore but turned it down because he was tired of long beards and robes.)
McKellan’s costar Orlando Bloom is famous as a blonde elf Legolas and the short haired occasional pirate Will Turner. He has yet to have a major hit in which he does not swing a sword.
Michael Landon: Little Joe Cartwright, Charles Ingalls, Jonathan Smith.
James Garner: Maverick (1957 - 1960) and The Rockford Files (1974 - 1980)
A fairly early one: Robert Young as Jim Anderson (Father Knows Best, 6 seasons) and as Marcus Welby, MD, for 7 seasons.
Roddy
Christopher Lloyd: Dr. Emmett L. Brown and Jim Ignatowski
Richard Chamberlain as Young Dr. Kildare and the priest from The Thorn Birds, Ralph de Bricassart
Caroll O’Connor as Archie Bunker and Bill Gillespie.
You could throw in TJ Hooker for Shatner as well.
Bea Benaderet must have held some sort of record for the most TV work of any actress of her day. (It’s been since supplanted I’m sure, but then she’s been dead for 42 years.)
Roles she’s equally remembered for in no particular order: Kate from Petticoat Junction, Cousin Pearl from The Beverly Hillbillies, and the voice of Betty Rubble from The Flintstones, in addition to which she had any number of lesser TV roles. (She was almost Ethel on I Love Lucy but passed due to contractual obligations and a dislike of Lucy [whom she’d worked with in radio].)
Julia Roberts won an Oscar for Erin Brockovich and has been in any number of movies but her “Come and knock on our door…” roles will always be two back to back early ones: Shelby in Steel Mangolias and Vivian in Pretty Woman.
YMMV, I guess, but I think most people associate Shatner with Star Trek a lot more strongly then with Boston Legal. Kirk takes up a lot of space in the pop-culture hivemind, it would take a pretty big hit to match it.
George C. Scott’s had two iconic roles, in Patton and Dr Strangelove.