Norma Jean & Marlyn was an HBO movie featuring Ashley Judd as Norma Jean and Mira Sorvino as Marilyn. I’ve not seen the movie, but apparently they play it like different aspects of Marilyn Monroe’s personality fighting each other for control.
Hijack
[Sampiro blinks and double checks his gaze to assure that he is seeing correctly, then hurls himself at the ground, grabs her knees, and calls out to his nearest manservant “Slaughter the fatted calf! Bring harpists and flautists and guitarists and harpsichordists from the village! Let the wine pour like rain in Seattle and let there be dancers of Chippendale quality brought forth! Call forth the sprites of Cole Porter and Busby Berkeley and commission from them a new song and dance! She lives! She lives!”}
Norma Jean and Marilyn had Ashley Judd and Mia Sorvino playing the same character.
An unusual example of an adult character being played as a child occurred in Jay and Silent Bob Strike Back. Kevin Smith cast his daughter Harley to play his character, Silent Bob, as a baby.
If Casino Royale counts, then it’s the most actors playing a single character ever, particulary at the end.
Pretty much any movie featuring magical or sci-fi shapeshifters, too.
In ]i]Star Trek III*, Spock was played by five different actors as the character rapidly aged, plus an extra one credited for “Spock screams”.
'Excuse me while I change."
The pre-Kathy Ireland (named “Spinach Destiny” in the credits) was Allyce Beasley, best known for playing secretary Agnes DiPesto on Moonlighting.
And so as to post a non-hijack, Shallow Hal (not to be confused with BBC’s Six Wives of Henry VIII, where amazingly enough the obese and old Henry was indeed the same actor who played the young athletic and shallow King Hal).
Damn, I just remembered.
In South Park, Bigger, Longer and Uncut, according to the credits, three actors did the voice for Ike.
Though it could be a joke, because Ike doesn’t exactly have a lot lines.
The Doctor Who TV movie with Sylvester McCoy & Paul McGann.
I can’t think of any movie besides those that have the same character at different ages, but it MIGHT be somewhere in the OP’s interest to know that Robert DeNiro and Marlon Brando both won the Oscar for playing the same character in two different movies: Godfather and Godfather II. (Both played Vito Corleone). I think that’s the only instance of THAT.
Big Fish - the main character is played by Ewan McGregor as a young man and Albert Finney as an old man.
Plan 9 from Outer Space.
Bela Lugosi died of a drug overdose during production and was replaced by a look-alike stand-in partially hiding his face behind the Dracula cape.
“American Splendor” had an odd 4-way combination (from IMDB):
Daniel Tay as Young Harvey
Paul Giamatti as Harvey Pekar
Harvey Pekar as Real Harvey
Donal Logue as Stage Actor Harvey
There were also 3 "Joyce"s and several other characters were duplicated as actors and as themselves.
Cleveland will do that to you.
Well, the grandaddy in that category would have to be The Five Doctors, featuring five incarnations of the character, though the fourth one was kind of a cheat, limited to archival footage.
The feat is somewhat matched by Kate Winslet and Gloria Stuart both being nominated for acting Oscars for playing the same character in the same movie; Titanic.
That was Gwyneth Paltrow as both the fat and thin versions of her character; she just used a fat suit for the former.
D’oh! I just realized you weren’t talking about her character, but other ones (like the nurse), in which case you are correct.
Godfather Series …oooh, good call… Forgot about that one!
Plan 9 from outer space…another good one.
It can include a series or sequel.
Keep them coming.
It seemed at times like each of the actresses played each of the female roles in Mulholland Dr.
The Incredible Hulk TV movies (Bill Bixby & Lou Ferrigno)
Swamp Thing (Ray Wise & Dick Durock)
Four if you count Bob Anderson who did most of the Swordfighting.