That's all I can think of. There isn't really one band who have had the same impact in prog, except a few instances such as the first King Crimson album, The Yes Album, Foxtrot and a few others

What he said.

Besides the obvious "The Beatles" answer...

I agree.

I don't really go along with this completely.  While there's no doubt about the impact Beatles had on rock, in terms of shaping the genre in its early days, they were hardly the only band or artist of great significance.  Rolling Stones were probably more important from the point of view of popularising rock as a kind of driving, angry music which Beatles seldom were in the pre-Rubber Soul days.  Bob Dylan popularised the idea of rock as a vehicle to register protest or at least weigh in on issues of social significance.  In terms of the one big bang event that shaped prog in its archetypal 70s form, it would have to be King Crimson and their ITCOTCK album. 

In your OP you say it clearly, 'regarding the artist's influence and popularity'. It would have to be between ELP and Yes then, they were the 'rock stars' within Prog at their peak.

As influential as KC or Genesis were, they never had that aurea of 'rock stars', I would even put Floyd on top of them if this is the question.

Back to Procol Harum, seeing as how they made one of the biggest selling singles with "A Whiter Shade Of Pale", they really must have had some influence on their millions of listeners. Also very innovative, seeing as that single was before "Sgt. Pepper" and they released the first ever real prog-rock epic in my mind (In Held Twas In I), etc. Moody Blues is up there too.

I'm not saying Radiohead isn't extremely influential but just like hundreds of thousands of more or less ambitious bands they are in debt to Pink Floyd. Saying that Pink Floyd didn't have a mainstram following doesn't make any sense. I hardly know anyone why didn't discover them through a couple of albums by them in their parents collection, and I actually think they've sold more albums than Beatles (with both Dark Side and The Wall among the 10 biggest sellers ever). 

This--plus they are the only real prog band that consistently crafted good hit short pop songs like the Beatles.

 

That works for me for the most part but I think the Moody Blues with their use of the mellotron sound certainly influenced many also as well as their 'themed album' style. And Floyd must have had a solid influence on many bands also.

!

 

I do not think that The Beatles were that much more important in "music", than anything else out there. For the time span, and specially in the 50's, film, literature and a lot of art, got around.  But what The Beatles, and they are not the only ones, did the most, was help break the control of the arts by an upper class crust ... that still thought that "popular music" (or popular anything!) was not a valid artistic concept or idea.

 

What they brought about ... go look at the two worst business decisions EVER done, on the Internet! Thus, what The Beatles, The Rolling Stones and othes brought about was that there was a business in the "popular arts" that were not quite considered before.  Their becoming famous helped bring out so much media about the popular music, that 10 years later, the previously important arts were not even selling 1/5th the amount of the stuff out there, and today, classical music is less than 1/10th of the music bought and sold out there, not to mention that you will never find a Lollapaloosa of Classical music anywhere either!

 

For your question, I think, the time, the place, the politics, and the arts, were way more important than any of the bands that we can think of. To say that Genesis or Pink Floyd were important, is like saying that you never saw "Tonite We All Love in London" and realize all the movie folks, literature folks, art folks and everyone else being around, getting to know each other and in many ways sharing ideas and fun along the way. That is far more important to Genesis, than the Beatles were! Why? Because it validates the time, the place, and the work you want to do.

 

Robin  Williamson has said that in many ways the psychedelic thing, or anything else was a media creation, because there are many folks in that midst that are true artists, and they will do what they do, and not care what else is going on. That means that the individualistic personality, is important to make something come alive, and I believe, trully, that this was the secret behind "progressive", and not anything else. Yes, no one can ignore The Beatles, or any other music at the time, but that like saying that you, or I, can not have opinions, because we were all born later, or worse ... not a part of the click ... how cliche and boring that is, PA! Don't you agree?

I'd have to agree.  The Beatles were truly revolutionary, all the way back to the haircuts, fashions & huge concert draws.  

Most of the other early prog bands could lay claim to the huge concert draws and success with AM radio singles, particularly Yes, ELP and Pink Floyd.  

If I were to pick one, I'd say Yes for their influence on prog song structure (complex timing changes, vocal harmonies etc.), instrumentation (Rick bass, Mellotrons) and success in the pop music world, all the way to 90125.  I rather detest "Owner" but we can't deny the HUGE impact it had on the resurgence of prog pop!  

Tendencies became apparent on Yesterday and Today and Rubber Soul and started bubbling to the surface on Revolver.

Sgt. Pepper and Abbey Road, IMHO, are critical compasses that helped other musicians choose their production values, assert compositional freedom, and employ a variety of interesting lyrical ideas. The Beatles were instrumental for creating the commercial environment in which prog could develop and prosper.

The Beatles planted the seeds and fertilized the garden. Pink Floyd, Hendrix, and many others also were essential parts of the 1967 revolution - music does not progress in a vacuum. The Beatles brought the clout and the savvy in a way that nobody else could deliver.

The rest is history - which, thankfully, is still being written.

Sadly this is correct.

In a world without an alphabet, every album would have a title like Led Zeppelin IV's and every act would be known as "The artists' formerly known as ________."

nope King Crimson

Yes = The Beach Boys

and then Pink Floyd are the Pink Floyd are prog

! Still an accurate comparison!

its true although many seem to dismiss the later 'version' of Genesis as influential. 

 

 

And to be honest, I never considered PF prog before coming to PA.

Check out 7 and 7 Is by Love from 1966 and see if you still believe that (not sure I consider any of them to be metal myself though. To me its early Heavy Rock).

https://www.youtube.com/watch?v=6An7KGK6U3c

But they're not a prog band by any stretch of the imagination, so they can't be the Beatles of prog.

I suppose you could say King Crimson though, within the subgenres of prog. Their early period had traces of just about all of it.