I dunno, they had that “flower power” song. 
Well the Who actually had exploding drums on live TV.
If it ain’t AC/DC (which it is), then it’s Motorhead.
They’re not hard as a rock, but they are thick as a brick.
See, to me, the Who are one of the original hard rock bands. If I were forced to slot them in one genre, it would be hard rock – few bands, if any, rocked harder than they did. Like one Doper once quipped “most bands play with each other; the Who played against each other.” Just because they had other colors in their musical palette doesn’t mean to me they are not, at heart, a hard rock band, at least in the Keith Moon years. (I don’t listen to anything post-Moon. When he died, the Who became a different band.)
I’m really confused then - Why is Metallica not mentioned?
And no mention of Boston?
Is it possible that Metallica is considered a Metal band?
Indeed - give or take. 
Oh - Heart coffee ad!
No - two of them!
Boston was mentioned by @Gatopescado.
I personally don’t find them to be particularly “hard.” I’d call the arena rock But I don’t really think of them as “hard rock.” This could just be me, as I know they are lopped into that genre sometimes/often.
Metallica is heavy metal, specifically thrash metal, but you can make “metal” a subset of “hard rock” here if you want. It depends on if you’re a lumper or a splitter in terms of musical genres. I consider metal separate from my idea of hard rock, but it’s a little difficult for me to define it succinctly.
To those who say Cream, I hope Ginger and Jack pay you a visit tonight. Even Eric acknowledges they were a jazz trio.
I don’t care what Eric says, they were in no meaningful way a jazz trio.
Outside nomination of The Cult. Because I like them and I can’t stand AC/DC.
Just … no.
Not in a million years.
That was Butt-Head who wore the AC/DC shirt. Beavis wore the Metalica shirt.
I think AC/DC would have to be it. I skimmed through my albums and most other artists changed through their careers, AC/DC stayed pretty consistent throughout. Motorhead would be up there, though Lemmy always said they were a Rock and Roll band.
Among his other issues, Eric wouldn’t know jazz if it bit him on the butt.
Aw jeez, I’m even dumber than those two idiots.
Their last single. Isn’t anything with a flute jazz?
Remember when Eric walked out of the Yardbirds because “For Your Love” was too poppy?
Eric never was/isn’t a jazz musician, but Ginger and Jack were and they both have stated their playing in Cream was based in jazz. Ginger’s original concept for Cream was a jazz trio. Eric went in thinking it would be blues trio, actually quartet because he wanted keyboards, which he got in Blind Faith. It evolved to whatever you want to call it except hard rock as we think of it today.
Also, I should have clarified that Eric’s “admitting” it was a jazz trio is a kind of joke because of what Ginger and Jack have been saying for decades.
“I thought of Cream as sort of a jazz band,” Jack Bruce said, “only we never told Eric he was really Ornette Coleman.”
https://www.rollingstone.com/feature/how-cream-defined-the-rock-power-trio-190712/
"Despite his rock bona fides, Baker always insisted that Cream were a jazz band. “Oh, for God’s sake, I’ve never played rock,” he told jazz.fm in 2013. “Cream was two jazz players and a blues guitarist playing improvised music. We never played the same thing two nights running … It was jazz.”
And I know heavy metal is different from hard rock.
“I’ve seen where Cream is sort of held responsible for the birth of heavy metal,” Baker said in a typically caustic 2015 interview. “Well, I would definitely go for aborting. I loathe and detest heavy metal. I think it is an abortion."
Well, I respectfully disagree with the cantankerous but talented Mr. Baker. He most definitely did play within the rock idiom behind the kit, whether he likes to admit it or not. Yes, it was through the lens of jazz background and technique, but he played rock music. There is nothing about rock music saying it cannot be an improvised form. They very clearly have song structures, they may mix things up, but – and it’s all a continuum – to me it’s clearly rock-based with jazz influences vs the other way around.
He just has some bee in his bonnet about being called a “rock” band for whatever reason – he sees it as somehow derogatory. Whatever. I don’t listen to what he says, just what he plays.
If you had to explain to the aforementioned alien more precisely what is meant by hard rock, what modes/keys/rhythms/instruments/chord progressions/structures characterise it?
That’s not how I see it. Metal is hard rock.