I get this impression about Keanu Reeves that he has virtually no ego - at least relative to other actors - and is constantly surprised by his own success.
Lash Larue, an cowboy actor of the 40s known for using a whip, was known to be an ass in the days of his stardom. In the 50s, his career dwindling, he took out an ad in Variety asking for work, and admitting he had been a jerk but had changed.
I remember an interview with Steve Martin while he was shooting (I think) Dead Men Don’t Wear Plaid. He said something to the effect of “I’m starring in a musical. The problem is, I can’t sing, I can’t dance, and I can’t act.”
Acknowledging that they aren’t the most popular:
Bruce Campbell, who wrote “If Chins Could Kill: Confessions of a B Movie Actor.” Also said elsewhere.
Kathy Griffin, who starred in “Kathy Griffin: My Life on the D-List.”
A mildly surprised, yet not quite knowing what’s going on or why is how most of his characters “look” as well 
No clue, but I think the place to look would be other celebrities who took up acting after they got famous. I can’t imagine that musicians and comedians are so innately good at performing that almost half of all celebrity actors come from their ranks. They got famous by another path first, then Hollywood recognized them as a draw. Their acting talent was a secondary consideration, at best.
Robert Mitchum never went so far as to say he was a lousy actor (he wasn’t), but he was on the record saying that being a movie actor wasn’t so special. One of his favorite wisecracks was, “For years the biggest star in the world was Rin Tin Tin. Can’t be much to it if a dog can do it.”
Character actor Edgar Kennedy once said, “I overact. I know I overact” and said that he depended on the director to tell him to dial is back.
I can’t think of any actors who ever said, “I can’t act. I have no talent. I stink.”
On the other hand, I have heard some pretty GOOD actors acknowledging the limits of their talents, and saying, “I’d really love to do a part like such-and-such, but I know I’m just not good enough to do that.”
George Clooney is a very solid, capable actor in the right parts, but he’s admitted that, for instance, he doesn’t have the skills or talent to do what Daniel Day-Lewis did in My Left Foot.
Years back, Roger Moore tried to do a musical in London’s West End, and I remember that he dropped out during rehearsals, admitting humbly that he couldn’t sing well enough to carry the show. He said he liked and respected the producers and his co-stars too much to continue, and quit so there’d be time to find a more talented replacement.
I would argue against you on this one.
I don’t think acting is that particularly hard of a job, but being an actor is a trying one.
I remember David Spade (I know, I know) on a late show some night talking the actress from Precious and he was saying (paraphrasing) “I wonder how long it will take for people to know that it’s not hard to do what we do. I mean, look at her…she walks off the street and has an Oscar”. It’s not that hard to act, but being a professional actor is difficult (as you said above)
I’m drawing a blank on names at the moment, but a lot of comedians-turned-actors have very little ego about their acting talents. Listening to interview shows like WTF and You Made it Weird over the years, I know I’ve heard several variations on, “I’m not much of an actor, but I know how to show up and do what they hired me for.”
Years ago I saw James Garner (Maverick, Rockford Files etc.) on the old Bob Costas hosted *Later *show. Costas asked him about method acting etc. and Garner just kinda laughed and said something to the effect of, “Nah, I just make sure I learn my lines and hit my marks and get paid…”
Tim Allen and Ray Romano, among others, have said almost this very thing.
Reportedly, when Mitchum was asked about acting, his response was, “It sure beats working.” I was just googling to get a cite for that, and I see that a biography of him is titled It Sure Beats Working.
I seem to recall some Very Handsome Actor recently saying something about how he knew he was hired for his looks and that his acting was not that great. But I can’t find it now. I want to say it was Channing Tatum, maybe around the time The Eagle came out. But I can’t find it now. Does that sound familiar to anyone else?
He’s not the only one.
I like him and he seems really cool, but there was no way to pass that up.
Whether one thinks he’s a good or bad actor (he’s had huge hits and huge misses), there is something different, something special about him. He’s not a cliched publicity mad, boozing, drugging, loud mouthed pussy hound, dating the starlet of the week, showing up on talk shows plugging his movie, or getting in brawls in bars. A bit of a mystery, Keanu is. His exotic looks and quiet demeanor don’t hurt.
Bear in mind that Keanu gave *$80 million *out of the $114 million he earned from the Matrix movies to the films’ special effects, makeup and costumes staff, because he said he already had enough money and he thought they deserved it.
I don’t think Michael J. Fox ever would have denied that he spent his whole career playing Alex Keaton – Alex Keaton travels through time, Alex Keaton goes to Vietnam, Alex Keaton moves to Manhattan and does lots of drugs . . .
He added that they should be excellent to each other, and party on.
Chevy Chase has admitted that he’s by no means a brilliant actor.