I know this doesn’t have a definitve answer so here it is.
What was really the hardest rock band ever?
Peter Rock and the Fossils?
Your question puts me in a hard place.
My nominees:
Led Zepplin
Rolling Stones
Jimi Hendrix
They all pointed in the direction others would follow.
While this is clearly a poll of sorts, this is the sort of specialty question better suited to Cafe Society. . .where you will next find it.
[ /Moderating ]
I think you’ll have to refine your question a little to get a meaningful answer. If you mean the hardest music by any rock band, the answer is going to come from one of the sub-genres of metal (“death metal” or “black metal” or something similar).
But, if you leave metal out and ask who is the hardest of the “hard rock” genre (as per definition on wikipedia) you should get answers from this list. From the bands I’m familiar with on the list (almost all of them) I’d say it’s between Motorhead, Iron Maiden, Black Sabbath, or Zakk Wylde’s Black Label Society. I’m quite sure YMMV.
I don’t know how some of the bands belong on that list (Wings?), but let me be the first to say Jethro Tull 
I think you have to consider the timeframe and context in which the group played.
These days, pretty much anything goes and we have loads of technology to realize it.
In light of that, I’d nominate The Kinks. *When You Really Got Me * came out, there wasn’t anybody doing anything even remotely as hard as that. They didn’t even have the equipment for it; Dave Davies had to slit his amp’s speaker cones to get that nasty sound. As you go further along in time, you have many bands beng “hard” on purpose, so it’s harder to distinguish between them.
I don’t think you can reasonably describe those bands as playing rock, so I wouldn’t nominate any of them.
That’s a better set of choices, but as was mentioned, you really have to consider where the music was relative to what had come before. You also have to consider how well that impact can be appreciated today. The band with maximum points in both categories wins the contest.
For my money, I’m going to have to nominate Led Zeppelin. Most of the hard rock bands before are a little tough to identify as hard rock for those of us who grew up after the 70s, and none of the bands afterwards (with the possible exception of Black Sabbath) were quite the departure from what had been done before.
While Led Zep is more hard rock than heavy metal by today’s standards, at the time they were considered, along with the Sabs to be heavy metal.
I would nominate Guns n’ Roses - hard, sloppy in the right ways, blues based and dangerous…
Where to begin?
Heavy metal (whatever the sub-genre) isn’t rock? What the hell is it, then? If by your statement you mean metal is not the same genre as hard rock, well that’s why I excluded them in the first place. (well, that, and because I’m not a big fan.)
And with all due respect to An Arky (a fine musician, a scholar and a gentleman 
), I don’t see what relativity to previous music has to do with the OP. I remember hearing people say they preferred the Beatles to the Stones because the Stones were “too hard rock”. Do either of them merit inclusion now? Nor do I see how current appreciation of a band’s impact has any bearing on the question posed. Without question Zeppelin influenced everyone who came after. But Wagner influenced them (I have to believe. Could there have been an “Immigrant Song” without a “Ride of the Valkyres”?) Does he count?
With no empirical definition to “hardest” or even “rock”, no objective answer is possible. (It says so right there on the package.) There is no contest, only subjective opinions to a subjective question.
I don’t mean to come off as beligerent here. I just think there are many ways to read the question. Initially I was going to answer as though “hardest” meant most difficult to play. But I know how much board residents hate smart-ass answers. 
Hotblack Desiato.
Metal. It’s a distinct style of music that has significant overlap with rock, but there are some parts that definitely don’t belong there. As always, genre lines are nebulous, but it’s very difficult to say that Ephel Duath plays rock and claim that avant-garde jazz is not rock (which I think most people would agree with).
My vote goes to Led Zeppelin. They show a strong blues influence that tips them towards the rock category in my mind.
I would say Black Sabbath. They took what Zeppelin started and made it heavier, darker, and harder than ever before.
If we’re going to say that heavy metal is not hard rock, then I’ll nominate AC/DC. Nothing there but straight forward, in-your-face, rock ‘n’ roll.
Thanks, no sweat. This thread is so subjective, I think there are cases to be made for lots of bands and there are as many opinions as there are sphincters…
I do think there has to be some comparison to what was going on at the time, though, otherwise, today’s death metal bands would win out in terms of guitar density per second, lack of ballads per album or whatever. Although, in a way, today’s stuff could be discounted because so dang much compression (?) is used that it makes just about any hard rock from the 60s/70s sound like Herman’s Hermits in comparison, production-wise.
Also, I think attitude/walking the walk should have some influence, as well. There are some bands today that rock harder than hell, but probably still live with their moms.
Ah yes! Lead singer of the hardest hard rock group ever in any galaxy, Disaster Area.
Well… rock isn’t very hard if that’s where you end it. So the hardest rock band should be just under metal right? Well… I guess the hardest rock band, it the almost metal but not quite metal band.
Other then that, I haven’t listened to any real rock music for a while now.
Dude, I would suggest you point your quest in the direction of The Melvins and St Vitus.