He does have a ‘type’ these days, but unlike most (maybe all) of the people mentioned here, I think he’s capable of being really moving and convincing all the same. He brings some kind of depth to those characters that I’m not sure anyone else does.
Well, in the cases of Chico and Harpo at least, they definitely weren’t playing themselves, since Chico did not speak with an Italian accent and Harpo was quite well spoken.
The first 3 coming to mind for me were Hugh Grant, Edward G Robinson (both already mentioned) and Steve martin.
Martin even.
Kate Hepburn sprang to mind when I read the post title. Of course. 
All these answers, and not one mention of Nicholas Cage?
Whether Chico spoke with an Italian accent in the movies is debatable. 
But yes, that’s true.
Ooh, good one. I’d forgotten all about him (and now, thanks to you, I’ll have to try and erase him from my mind again).
How does that guy keep getting work? Not only does he play the same guy, the guy he plays isn’t even likable!
I used to work in a video store. I STILL maintain that Cage has made a total of 4 good movies (Fast Times at Ridgemont High, Bringing Out the Dead, Matchstick Men - which is made watchable by Sam Rockwell, and Raising Arizona). And that his Oscar should be revoked, and given to its rightful owner, Sean Penn, for Dead Man Walking.
Will Farrell. Zero range as an actor, no sense of comedic timing, and not funny even when he was at his prime doing his cheerleading character on SNL. His agent must have told him that he should base the remainder of his painful acting career on that character. I think it’s pretty discouraging that actors like him have come to be praised for their “comic genius” in a world of so much talent, and I find myself at a loss of words when I wonder how someone as talentless as he is gets so much work trying to be a “lovable baffoon” when he’s really nothing more than an obnoxious, vulgar clod.
I also appear to be in a distinct minority with this opinion.
Matthew Perry.
I can’t think of a better example than Charlie Sheen.
Joe Pesci
Denis Leary
Adam Sandler
Sinbad
Will Smith (although he does a fantastic job of playing himself)
Robin Williams
I’m not much of a classic movie expert, but Marilyn Monroe pretty much always played herself, didn’t she?
You may be in a minority, but you’re right. But then popular and talented being two different things is nothing new. (Although I can’t say he’s never made me chuckle on SNL.)
Oh, and I forgot to put on my list:
Elvis
Jim Carrey - He’s pretty much the Ace Ventura/Mask character most of the time (with notable exceptions - I thought his performance in The Truman Show was rather refreshing.
Richard E Grant - He’s always Withnail.
Jack Nicholson surprised me in About Schmidt, where he plays a depressed, ineffectual loser - I can only imagine that the surprise at this unusual choice of character was the reason for the critical acclaim over this movie, as it was just sort of… meh.
Cary Grant
James Stewart
Gary Cooper
John Wayne
Clint Eastwood
I have to disagree with the OP - I don’t consider having just one character to be “bad acting”, just a different kind of acting. Chameleonhood is not the be-all and end-all of the thespian arts. I don’t care much how an actor acts in a different movie than the one I’m watching, I just want to see him really sell the scene. If he then plays basically the same character in his next film, that’s OK, so long as he does a good job then, too.
Frankly, as far as I’m concerned, a lot of all those “character” mannerisms, accents and whatnot is just showing off. Stand on your mark and speak your lines like you mean them, and don’t worry about the rest.
It’s typecasting, isn’t it? (albeit a special case of typecasting, where the type happens to be the actor’s natural personality, as far as we are able to ascertain).
I’d have to say Alec Baldwin. His presence completely takes me out of the movie.
I loved The Aviator till he showed up.
Clark Gable! I can’t believe I forgot him.
Can one of our movie buffs confirm or deny this rumor: the reason he didn’t win the Oscar for Gone With the Wind is that it was widely believed that he was just playing himself.
Execellent point. And, remember, being a chameleon means respect but lower pay. It’s only when your recognizable to audiences that you can become a star, and it’s rare to do that by being different in every film (Meryl Streep managed, but few others).