Poll Suggestion: There's More Than One of Them...

 
? ?
 
White Comanche (1968)
https://www.imdb.com/title/tt0061497/reference
William Shatner ... Johnny Moon / Notah
Plot
Twin brothers, half white and half Comanche, take different paths that overlap
William Shatner plays two roles:
cowboy Johnny Moon and his ruthless Indian twin brother, Notah.
Notah likes peyote and ...
 
Trivia
his film is listed among The 100 Most Enjoyably Bad Movies Ever Made
 
Filming Locations
Spain
   
https://www.imdb.com/title/tt0061497/ratings
623 IMDb users have given a weighted average vote of 4.1 / 10


https://www.imdb.com/title/tt0061497/mediaviewer/rm2690659584
- - -
  
Star Trek: The Original Series (TV Series)
Operation - Annihilate! (1967)
https://www.imdb.com/title/tt0708441/reference
William Shatner ... Capt. Kirk / Sam Kirk
- - -
  
Star Trek: The Original Series (TV Series)
Return to Tomorrow (1968)
https://www.imdb.com/title/tt0708445/reference
William Shatner ... Capt. Kirk / Sargon
.

Nia,

For your consideration:

Bewitched (1964–1972)
https://www.imdb.com/title/tt0057733/characters/nm0000548
Elizabeth Montgomery as Samantha Stephens and Serena (paternal cousin of Samantha)

Diagnosis Murder (1993–2001)
https://www.imdb.com/title/tt0105986/characters/nm0001813
Dick Van Dyke as Dr. Mark Sloan, Gangster John 'Mr. G' Gotti, J. Edison Nash, Jonathan Nash, Judith Nash, Julian Nash

The Man in the Iron Mask (1939)
https://www.imdb.com/title/tt0031619/characters/nm0371775
Louis Hayward as Louis XIV and Philippe of Gascony

Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb (1964)
https://www.imdb.com/title/tt0057012/characters/nm0000634
Peter Sellers as Group Capt. Lionel Mandrake, President Merkin Muffley and Dr. Strangelove

7 Faces of Dr. Lao (1964)
https://www.imdb.com/title/tt0057812/characters/nm0709704
Tony Randall as Dr. Lao, The Abominable Snowman, Merlin the Magician, Apollonius of Tyana, Pan, The Giant Serpent and Medusa

The Mouse That Roared (1959)
https://www.imdb.com/title/tt0053084/characters/nm0000634
Peter Sellers as Grand Duchess Gloriana XII, Prime Minister Count Rupert of Mountjoy and Tully Bascombe

Mary Poppins (1964)
https://www.imdb.com/title/tt0058331/characters/nm0001813
Dick Van Dyke: Bert and Mr. Dawes Senior

Nia,

For your consideration:
Orphan Black (2013–2017)
https://www.imdb.com/title/tt2234222/characters/nm1137209
Tatiana Maslany: Sarah Manning, Cosima Niehaus, Alison Hendrix, Helena, Rachel Duncan, Beth Childs, Krystal Goderitch, MK, Jennifer Fitzsimmons, Katja Obinger...

... a more complete list ...

https://en.wikipedia.org/wiki/List_of_Orphan_Black_characters
Sarah Manning, Cosima Niehaus, Alison Hendrix, Helena, Rachel Duncan, Elizabeth "Beth" Childs, Krystal Goderitch, Veera "M.K." Suominen, Pupok (voice) [a], Katja Obinger, Tony Sawicki, Jennifer Fitzsimmons, "Church Clone" and Camilla Torres

Wait - in the whole wild, wacky, unrealistic show of Dallas, there was never a look alike or an evil twin????  I'm disappointed.

Nia,

FYI:
https://www.nydailynews.com/entertainment/movies/10-performances-actors-playing-multiple-roles-films...

For your consideration from this article not already in your list:

Legend (I) (2015)
https://www.imdb.com/title/tt3569230/characters/nm0362766
Tom Hardy as Reggie Kray and Ron Kray

Cloud Atlas (2012)
All of the core actors in this film take on multiple roles as the plot spans across six different short stories.
https://www.imdb.com/title/tt1371111/characters/nm0000158
Tom Hanks as Dr. Henry Goose, Hotel Manager, Isaac Sachs, Dermot Hoggins, Cavendish Look-a-Like Actor and Zachry

https://www.imdb.com/title/tt1371111/characters/nm0000932
Halle Berry as Native Woman, Jocasta Ayrs, Luisa Rey, Indian Party Guest, Ovid and Meronym

The Social Network (2010)
https://www.imdb.com/title/tt1285016/characters/nm2309517
Armie Hammer as Cameron Winklevoss and Tyler Winklevoss

Enemy (2013)
Jake Gyllenhaal as Adam + Anthony

FYC:

Fan (2016) - Shah Rukh Khan as Gaurav Chandna and Aryan Khanna


Don (2006) - Shah Rukh Khan as Don and Vijay


Bãhubali: The Beginning (2015) - Prabhas as Shivudu and Baahubali


Dhoom 3 (2013) - Aamir Khan as Sahir Khan and Samar Khan


Bãhubali 2: The Conclusion (2017) - Prabhas as Shivudu and Baahubali


Enthiran (2010) - Rajinikanth as Dr. Vaseegaran and Chitti


Kaminey (2009) - Shahid Kapoor as Guddu and Charlie

? ?
 
Blazing Saddles (1974)
https://www.imdb.com/title/tt0071230/reference
Director: Mel Brooks  
Writers: Mel Brooks,
Mel Brooks ... Governor Lepetomane / Indian Chief

https://www.imdb.com/title/tt0071230/mediaviewer/rm514964481

https://www.imdb.com/title/tt0071230/mediaviewer/rm3793590017
.

? ?
  
The Wizard of Oz (1939)
https://www.imdb.com/title/tt0032138/reference
Judy Garland
Frank Morgan ... Professor Marvel / The Wizard of Oz / The Gatekeeper / The Carriage Driver / The Guard
Ray Bolger ... 'Hunk' / The Scarecrow
Bert Lahr ... 'Zeke' / The Cowardly Lion
Jack Haley ... 'Hickory' / The Tin Man
Margaret Hamilton ... Miss Gulch / The Wicked Witch of the West
- - -
  
Dorothy's Song - Covid-19 version
https://www.youtube.com/watch?v=C-7gZYT7MKg
.

In Kind Hearts and Coronets (1949) Alec Guinness played 7 characters, including Lady Agatha :)

Nia,

I am not suggesting that you replace any of the choices with this. But, I thought you might get a chuckle out of this television movie:

The Clone Master (1978 TV Movie)
In order to test the validity of his experiments on cloning, a scientist makes clones of himself, but it causes problems that he didn't foresee.

Likewise, even though I'm not suggesting you should use this for your poll, I suspect you would enjoy this episode of Red Dwarf (TV Series), Rimmerworld (1993).
https://www.imdb.com/title/tt0684176/plotsummary
The Starbug crew returns to the Simulant's battleship to salvage for food-supplies. But Rimmer, who has been diagnosed of a tense nervous disorder, escapes on-board a escape pod which has no steering. And is whisked away through a time-hole, only to find himself on a planet inhabited by clones of his own self.

FYC: Noomi Rapace as the seven Settman Siblings in What Happened to Monday (2017)
Charles Chaplin as Hynkel and a Jewish Barber in The Great Dictator (1940)
Nicolas Cage as Charlie and Donald Kauffman in Adaptation.(2002)
Eddie Murphy as Kitt and Jiff Ramsey in Bowfinger (1999)
Denis Lavant as 11 characters in Holy Motors (2012)

We have a poll which includes three or more roles: https://www.imdb.com/poll/VOHIc-32iAc/

Perhaps you could limit your list to dual roles, or make a separate list for television?

FYC:
Mark Ruffalo as Dominick and Thomas Birdsey in I Know This Much Is True (2020– )

FYC:
'Moon' with Sam Rockwell:
https://www.imdb.com/title/tt1182345/
I guess he is pretty much better than some of them on the list.
Role: Sam Bell / Sam Bell (cloning)

 
? ?
 
Sybil (1976-1976)
https://www.imdb.com/title/tt0075296/reference
A young woman whose childhood was so harrowing to her
that she developed sixteen different personalities is treated by a doctor.
Sally Field ...   Sybil
  
https://www.imdb.com/find?q=Sybil&s=tt&exact=true
.

Your discussion link doesn't seem to work.