Sure they are. But there are different kinds of comedians. The first episode of Shelley Duvall's Faerie Tale Theatre, The Tale of the Frog Prince was like a crossover between Mrs. Doubtfire and Tootsie since Teri Garr was in that episode with Robin Williams.

Are the women that you mentioned are they comedians at all? I know that Shelly Duvall co-starred with Robin Williams in Popeye where they played Popeye and Olive Oyl. But has anybody seen her lately in anything?

Shelley Duvall, Teri Garr, Madeline Kahn, etc.

Not much out of the ones that are alive today, can they improvise?

I have had a good think about this and I wonder if people even realise what a talented man Robin Williams was, he was a true actor that could bring not only joy but also feeling and sadness to the stage. I find it very hard to picture anybody else in this role. Kevin Spacey is somebody that can do great impressions and is a very talented actor. I think that if he tried he could give the persona of Mrs Doubtfire a soul. But nobody can replace Robin Williams.
Gentlemen, you can't fight in here! This is the War Room!

Ben Stiller? Lol

Where's JIm Carey and Ben Stiller? Fck outta here..

Match, no way, though I agree with others that John Candy comes close and I'll add Steve Martin. They all had/have roles in touchingly funny or serious films with very human characters with whom the audience could connect. All three were/are known outside of movies/TV as decent, generous men, which I think carries over when one watches their work.
Only Williams' talent was unique from the two others.
The rest of the list, while talented are utterly no match for Williams.

Sandler..really? You just have to watch Robin in One Hour Photo to realize he could portray so dark and lonely like no one else. He was a one of a kind talent. That scene in Good Will Hunting "it's not your fault"and every damn thing he ever did. John Candy maybe approached himbecause he had that same sadness beneath this overwhelming talent that couldn't handle this world. Stan Laurel? Gleason? There are only a few.

Two of my favorites are Adam Sandler and Jim Carrey.
Son, you got a panty on your head.

I don't think there's been anybody who was as instantaneously funny as Williams. He could literally just pull funny out of this air, at the drop of a hat, and just keep it going and going. And so, his improvisational abilities carried over into his films, and Doubtfire is no exception.
Others have kind of nailed with his "warmth". He was a guy you'd like to know and hang out with. His humor appealed to a broad group of views (virtually anybody). His comedy really is its own, unmatched brand. And he was literally a touchstone in people's lives for several generations. If you're 40 years or younger, think back and Robin Williams is there, at your earliest memories.

The thing about Robin was his warmth, you just wanted to hug him. Or be his child I always wanted a father like Robin, and that says everything. He was a funny, smart, witty and lovable man. All the other comedians you mentioned might be funny but they're not as lovable as he was. I think Mrs. Doubtfire was the first Robin Williams movie I saw, I was only 6 or 7 years old at the time, and I literally fell in love with him after watching him play there!

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Yeah, you're wrong on Candy especially and also on Ramis, although I'll grant you the argument that no one under 30 knew who Ramis was. But you're so completely wrong on Steve Martin it's ridiculous.

This 26-year old loves John Candy!

Well Harold Ramis and John Candy are already dead and no really curred. I dont think anyone under the age of 30 even knows who they are. Steve Martin is obviously the most well known of the bunch but I dont really see his boring , daddish humor leaving that much of a gaping whole in the entertainment world. William's raw passion and dedication to his artform was palpable and it really shone through in the reaction to his death. Theirs a difference between starring in a couple of good, well liked films and making a genuine lasting connection with the world as an artist and public figure

"Harold Ramis, Steven Martin, Chevy Chase, Martin Lawrence and John Candy: aren't as universally loved and known and havent really left a big enough mark on comedy"
Steve Martin and Harold Ramis (Egon in Ghostbusters, director of Caddyshack and Groundhog's Day) haven't left a big enough mark on comedy?!? John Candy isn't universally loved????

Harold Ramis, Steven Martin, Chevy Chase, Martin Lawrence and John Candy: aren't as universally loved and known and havent really left a big enough mark on comedy
Seth Rogen, Jonah Hill: too mean spirited and nichey. Their stoner/dudebro schtick is going to get old real fast
Adam Sandler: very popular but not that respected (despite a few fluke performances) Considered by many as a sellout
Eddie Murphy: Possibly, but then again he comes off as kind of commercially driven and not that well loved beyond his movie work
The only comedian that would come close is Jim Carey in my opinion. He has an undeniable universal appeal and his passion for comedy is positively infectious. He was also able to sink his teeth into more emotional, serious roles to great effect(ala The Truman Show + Eternal Sunshine of The Spotless Mind) His performances and eccentric lovable persona will always be remembered and his death will garner a very similar outpouring

As far as sheer acting talent alone, I think Williams was the best from your list. Acting wise, my list goes: Williams, Murphy, Murray, Candy, Martin, and the rest. I think the difference is those five are legitimate actors who happen to be funny, as opposed to the rest who are comedians who happen to act. Lawrence and Chase shouldn't even be on the list, imo.

I think Robin Williams and John Candy had something similar in their acting. Both were able to be hilarious, yet emotional and really make a person cry. The rest are really just funny, in my opinion. I've never gotten emotional in an Eddie Murphy film, but he is hilarious. I think what separates Robin Williams from the actors you mentioned is that not only was he a comedian, but he was incredible in dramatic roles such as Good Will Hunting, where he did not play a funny guy but was so good he was given an Oscar.