Gregory Peck
Humphrey Bogart
Gary Cooper
Clark Gable
Alan Ladd
Yul Brynner
Robert Mitchum
Cary Grant
Marlon Brando
Elizabeth Taylor
Viven Leigh
Katherine Hepburn
Audrey Hepburn
Sophia Loren
Meryl Streep
Judi Dench
Diane Keaton
Julia Roberts
“None” is a fair answer.
Don’t look at other replies until you’ve posted your own.
Gregory Peck: umm… none. Off to a great start…
Humphrey Bogart: Treasure of the Sierra Madre
Gary Cooper: none
Clark Gable: Rhett Butler
Alan Ladd: none
Yul Brynner: Magnificent 7
Robert Mitchum: Cape Fear
Cary Grant: Bringing up Baby
Marlon Brando: Apocalypse Now
Elizabeth Taylor: none
Viven Leigh: Quiet man
Katherine Hepburn: Bringing up Baby
Audrey Hepburn: Robin & Marian
Sophia Loren: Dirtier Old Men
Meryl Streep: Kramer vs. Kramer
Judi Dench: M (the character, not the movie)
Diane Keaton: Looking for Mr. Goodbar
Julia Roberts: Pretty Woman
Guess I haven’t watched as many old movies as I think I have. Bear in mind, I haven’t actually seen some of those movies… they’re just the titles I associate with the actors (Treasure of the Sierra Madre, Cape Fear, Dirtier Old Men, Kramer vs. Kramer, and Pretty Woman).
Gregory Peck - Boys From Brazil
Humphrey Bogart - African Queen
Gary Cooper - ??
Clark Gable - “Frankly, my dear…”
Alan Ladd - ??
Yul Brynner - The King and I
Robert Mitchum - ??
Cary Grant - NxNW
Marlon Brando - Stella!
Elizabeth Taylor - Who’s Afraid of Virginia Wolff
Viven Leigh - NxNW? Was she in that?
Katherine Hepburn - Bringing Up Baby
Audrey Hepburn - Breakfast at Tiffany’s
Sophia Loren - ??
Meryl Streep - Music of the Heart
Judi Dench - Shakespeare in Love
Diane Keaton - I don’t know what it is, but I can picture the hat
Julia Roberts - Ocean’s Eleven
Gregory Peck To Kill A Mockinbird
Humphrey Bogart Casablanca
Gary Cooper None
Clark Gable Gone With The Wind
Alan Ladd None
Yul Brynner The King And I
Robert Mitchum None
Cary Grant Arsenic and Old Lace
Marlon Brando Guys and Dolls
Elizabeth Taylor Cleopatra
Viven Leigh Gone With The Wind
Katherine Hepburn The African Queen
Audrey Hepburn Breakfast at Tiffany’s
Sophia Loren None
Meryl Streep Death Becomes Her
Judi Dench Goldeneye
Diane Keaton Annie Hall
Julia Roberts Pretty Woman
As Ethilrist said (though I promise I didn’t read his answers until I previewed), some of these movies I haven’t actually seen. Some are my favorites, and therefore not the first thing most would think of starring that particular actor.
Gregory Peck - Atticus Finch
Humphrey Bogart - Sam Spade
Gary Cooper - None
Clark Gable - Rhett Butler
Alan Ladd - None
Yul Brynner - The King of Siam
Robert Mitchum - None
Cary Grant - None
Marlon Brando - Don Corleone
Elizabeth Taylor - Cleopatra
Viven Leigh - None
Katherine Hepburn - None
Audrey Hepburn - Holly Golightly
Sophia Loren - None
Meryl Streep - None
Judi Dench - Jean (From As Time Goes By)
Diane Keaton - None
Julia Roberts - Her character in Pretty Woman
Gregory Peck – To Kill a Mockingbird
Humphrey Bogart – Casablanca (damn, wish it were Maltese Falcon, but it’s not)
Gary Cooper – um, he was in High Noon, right?
Clark Gable – GWTW
Alan Ladd – Shane
Yul Brynner – The King and I/Westworld (sorry, they really were pretty much that close together in my head)
Robert Mitchum – none
Cary Grant – Philadelphia Story
Marlon Brando – The Godfather
Elizabeth Taylor – Cleopatra
Viven Leigh – GWTW
Katherine Hepburn – The Philadelphia Story
Audrey Hepburn – Funny Face
Sophia Loren – none
Meryl Streep – Deer Hunter? Was she in that? It’s weird I can’t come up with anything fast on her. Sophie’s Choice, Bridges of Madison County…
Judi Dench – none
Diane Keaton – Annie Hall, of course
Julia Roberts – My Best Friend’s Wedding
I didn’t read anyone else’s responses yet, to avoid being influenced:
Gregory Peck - To Kill a Mockingbird
Humphrey Bogart - Casablanca
Gary Cooper - Meet John Doe
Clark Gable - Gone With the Wind
Alan Ladd - Shane (even though I don’t think I’ve ever seen it)
Yul Brynner - The King and I
Robert Mitchum - Night of the Hunter
Cary Grant - hard one; probably North by Northwest
Marlon Brando - On the Waterfront
Elizabeth Taylor - Who’s Afraid of Virginia Woolf?
Viven Leigh - Gone with the Wind
Katherine Hepburn - Philadelphia Story
Audrey Hepburn - Breakfast at Tiffany’s
Sophia Loren - None
Meryl Streep - another hard one; probably Sophie’s Choice
Judi Dench - actually, the TV series As Time Goes By
Diane Keaton - Annie Hall
Julia Roberts - Pretty Woman
Gregory Peck - none
(on preview: jeez, forgot about To Kill a Mockingbird)
Humphrey Bogart - Rick in Casablanca
Gary Cooper - none
Clark Gable - Rhett Butler
Alan Ladd - none
Yul Brynner - the King of Siam
Robert Mitchum - none
Cary Grant - none
Marlon Brando - The Wild One*
Elizabeth Taylor - Who’s Afraid of Virginia Woolf?*
Viven Leigh - Gone with the Wind
Katherine Hepburn - Guess Who’s Coming to Dinner*
(on preview: why the hell didn’t I say African Queen? I love that movie!)
Audrey Hepburn - Charade
Sophia Loren - none
Meryl Streep - Silkwood
Judi Dench - As Time Goes By
Diane Keaton - Annie Hall
Julia Roberts - Pretty Woman*
*a movie I have never actually seen
Gregory Peck - To Kill a Mockingbird
Humphrey Bogart - The African Queen
Gary Cooper - High Noon
Clark Gable - Gone With The Wind
Alan Ladd - Shane
Yul Brynner - The King and I
Robert Mitchum - Cape Fear
Cary Grant - Father Goose
Marlon Brando - The Godfather
Elizabeth Taylor - Cleopatra
Viven Leigh - Gone With The Wind
Katherine Hepburn - Rooster Cogburn
Audrey Hepburn - Roman Holiday
Sophia Loren - Grumpier Old Men
Meryl Streep - Silkwood
Judi Dench - one of recent the James Bond movies
Diane Keaton - Annie Hall
Julia Roberts - Mystic Pizza
Gregory Peck : Atticus Finch (To Kill a Mockingbird)
Humphrey Bogart : Philip Marlowe (The Big Sleep)
Gary Cooper : High Noon
Clark Gable : Rhett Butler (Gone With the Wind)
Alan Ladd : none
Yul Brynner : The Magnificent Seven
Robert Mitchum : none
Cary Grant : CK Dexter Haven (The Philadelphia Story)
Marlon Brando : Stanley Kowalski (A Streetcar Named Desire)
Elizabeth Taylor : Rowena (Ivanhoe)
Viven Leigh : Scarlett O’Hara (Gone With the Wind)
Katherine Hepburn: The African Queen
Audrey Hepburn : Holly Go-Lightly (Breakfast at Tiffany’s)
Sophia Loren :none
Meryl Streep: Karen(?) Silkwood
Judi Dench : Queen Elizabeth (Shakespeare in Love)
Diane Keaton : Annie Hall
Julia Roberts : Pretty Woman
To copy what others have said, some of these I haven’t seen and I certainly don’t think they represent the best role by the actor, just what I was able to think of.
Gregory Peck – To Kill a Mockingbird
Humphrey Bogart – Casablanca
Gary Cooper – High Noon
Clark Gable – GWTW
Alan Ladd – None
Yul Brynner – The King and I
Robert Mitchum – Night of the Hunter
Cary Grant – Bringing Up Baby
Marlon Brando – A Streetcar Named Desire
Elizabeth Taylor – Cleopatra
Viven Leigh – GWTW
Katherine Hepburn – Bringing Up Baby
Audrey Hepburn – Breakfast at Tiffanys
Sophia Loren – None
Meryl Streep – Sophie’s Choice
Judi Dench – When Time Goes By (If it has to be a movie, then “Shakespeare in Love”
Diane Keaton – Annie Hall
Julia Roberts – Erin Brockovich
Gregory Peck-Atticus Finch in To Kill a Mockingbird
Humphrey Bogart-Rick Blaine in Casablanca
Gary Cooper-Will Kane in High Noon
Clark Gable-Rhett Butler in Gone with the Wind
Alan Ladd-Shane
Yul Brynner-the King of Siam in the King and I
Robert Mitchum-Gen Norm Cota in the Longest Day
Cary Grant-Mortimer Brewster in Arsenic and Old Lace
Marlon Brando-Don Vito Corleone in The Godfather
Elizabeth Taylor-Cleopatra
Vivien Leigh-none
Katherine Hepburn-Tracy Lord in the Philadelphia Story
Audrey Hepburn-Eliza Doolittle in My Fair Lady
Sophia Loren-none
Meryl Streep-Joanna Kramer in Kramer Vs Kramer
Judi Dench-M in the James Bond movies
Diane Keaton-none
Julia Roberts-Vivan Ward in Pretty Woman
Say, Zeldar do you have your own answers?
Thanks for asking, but by now I have been tainted by all these others.
I will say that Shane and Boy On A Dolphin would be my answers for Alan Ladd and Sophia Loren, since few have had any response for them.
I have already thought of a dozen more actors (in both categories) for a follow-up thread if this one seems to be popular enough.
Atticus Finch
Rick in “Casablanca.”
The sheriff in “High Noon.”
Rhett Butler
Some noir movie. He’s got a trenchcoat on. “This Gun for Hire,” maybe?
The gunslinger in “Westworld”
The professor in “Bringing Up Baby”–specifically, I see him in the frou-frou dressing gown doing that high-jump on the “I just went gay all of a sudden” line.
The biker in “The Wild One”
Wearing that white prom dress in “A Place in the Sun.”
Scarlett O’Hara
Queen Eleanor in “A Lion in Winter”
Holly Golightly
The rest I draw a blank on an actual role. It’s more a sort of “actor image” than something specific.
Gregory Peck - Atticus Finch
Humphrey Bogart - Sam Spade
Gary Cooper - The Sheriff in High Noon
Clark Gable - Rhett Butler
Alan Ladd - Shane
Yul Brynner - The King of Siam
Robert Mitchum - Max Cady (Cape Fear badass)
Cary Grant - Roger Thornhill
Marlon Brando - Stanley Kowalski
Elizabeth Taylor - Cleopatra
Viven Leigh - Scarlet O’Hara
Katherine Hepburn - Rosie from African Queen
Audrey Hepburn - Eliza Doolittle
Sophia Loren - the gal in Arabesque
Meryl Streep - The gal in Deerhunter
Judi Dench - Queen Elizabeth
Diane Keaton - Annie Hall
Julia Roberts - Pretty Woman
The more I think about this, I think it could be “The Blue Dahlia” or “The Glass Key.”
Anyway, it’s not “Shane.” 
Now going back and reading everyone’s answers - this is a great thread! How interesting that the first thing I thought of for Sophia Loren was “Arabesque” but it wasn’t the first thing I thought of for Gregory Peck - even though they starred together. Must have been because I was 15 when I saw Arabesque and fell in love with “old” Sophia. Damn! she was hot!
The more I had to think about it, the more I realized that “old Sophia” was just such a phenomenon that she overwhelmed whatever she was in. I know I must have seen her in at least ten things, but none of them are stand-outs as movies. The Pride and the Passion is more memorable for Sinatra’s rug and that big old gun. She was in El Cid with Heston, right?
The very serious role in the Two Women movie may have been her most artistic one, but it’s down the list in terms of one you’d think of.
What’s the first role you think of for:
Gregory Peck Dr. Mengele, The Boys From Brazil
Humphrey Bogart Queeg, The Caine Mutiny
Gary Cooper Marshal Cane (Kane?), High Noon
Clark Gable Rhett Butler, Gone With The Wind
Alan Ladd Shane, Shane
Yul Brynner King of Siam, The King And I
Robert Mitchum - none
Cary Grant Thornhill, North By Northwest
Marlon Brando Stanley Kowalski, Streetcar Named Desire
Elizabeth Taylor Martha (I think…) Who’s Afraid of Virginia Woolf?
Viven Leigh Scarlett O’Hara, Gone With The Wind
Katherine Hepburn Christine (Christina?), Guess Who’s Coming To Dinner
Audrey Hepburn Eliza Doolittle, My Fair Lady
Sophia Loren Jimena, El Cid
Meryl Streep Mary Fisher, She-Devil (because of my recent thread)
Judi Dench none
Diane Keaton One of the women, First Wives Club (most boring movie ever… wife made me watch)
Julia Roberts Vivian, Pretty Woman