This is cheating, but…
Redd Foxx’s real name was John Sanford. “Fred Sanford” was the name of his real-life brother.
So, you could say that, on the sitcom Sanford and Son, he was using his own last name.
In that same vein, Diane Keaton played Annie Hall, and her real last name is Hall.
Jerry Seinfeld played Jerry Seinfeld on Seinfeld.
And Mario Van Peebles playing his father Marvin in Baadasssss!
And, of course, Neil Patrick Harris in the Harold & Kumar films.
I thought of an obscure one. Ming-na Wen played Senator Wen on Eureka. IMDb says the senator’s name was Michaela.
Sort of similar, TCM recently showed the 1935 film, Ruggles of Red Gap. The Ruggles of the title is Marmaduke Ruggles, a proper English valet who was in the employ of an earl. The earl lost Ruggles in a poker game in Paris to an American, Egbert Floud, of the small Western boomtown, Red Gap, Washington. Anyhow, the American is played by Charles Ruggles. (Later Charles Ruggles played the father-in-law of the banker Drysdale on The Beverly Hillbillies.)
Jensen Buchanan was hired to play Sarah Gordon on One Life to Live. Eventually the character married Bo Buchanan and became Sarah Buchanan.
Not quite the same thing, but Days of Our Lives couple Will and Sonny is known by the portmanteau WilSon. When the actor playing Will left the show, Guy Wilson was hired to replace him.
That would be Anthony W. Brimley.
And that would be Olive M. Osmond.
BTW, my new book on the topic is now available.
Awesome name!
This was actually the kind of thing I was looking for. Not actors playing a fictional version of themselves, or playing a relative with the same last name.
And I’m a little embarrassed that I didn’t think of this one because I was a huge “Night Court” fan back during its original run.
Drew Carey played “Drew Carey” on “The Drew Carey Show”.
And Desi Arnaz Jr. played Desi Arnaz Sr. in The Mambo Kings.
Barry Pepper played Ned Pepper in True Grit.
Esai Morales played Bob Morales in La Bamba.
ElvisL1ves, see post #19.
James Hong played Dr. Hong in The Golden Child. Plus a couple other similarly named characters.
I think you’d find a lot of this sort of thing among Asian actors, especially Chinese. American scriptwriters were notoriously lazy about naming Asian characters for many years.
There’s a lot of examples of actors playing a parent in a bio-movie, but so many actors have stage names. E.g., Sophia Loren played her mother, who had a different last name. So the examples given so far are more the exception than the norm.
Bumping to add: Arturo Castro plays Jaime Castro on Broad City.
On Raising Hope, one of the main characters is named Jimmy Chance. In a flashback a teenaged version of Jimmy Chance was played by Greyson Chance.
On Family Guy, the role of Mayor West is voiced by Adam West.
Matt Smith, who was the eleventh actor to portray Dr. Who, in the episodes “The Rebel Flesh/The Almost People” portrayed a doppelganger of the Doctor who told everyone present to refer to him as “Mr. Smith” - an alias long used by the Doctor when forced to give a name other than The Doctor.
Not quite what the OP is looking for, but some of the posters for Men in Black billed it as starring “Mr. Smith and Mr. Jones”.