If you had to pick one band to represent “hard rock”, which would it be?
Off the cuff, I’d go with AC/DC.
That’s a really good choice.
Zeppelin, baby!
I think of Zeppelin as being more heavy metal than strictly hard rock, but I think that they, and AC/DC, are excellent examples.
When do we start the Definition jihad?
Mmm, hard one. I think Cream.
Deep Purple should be on the list somewhere.
I agree, Led Zep is my first thought followed by Black Sabbath.
Good suggestions so far, I’d throw The Who in there as well for consideration.
It won’t be started by me. 
When I was younger, I didn’t really understand the difference between “heavy metal” and “hard rock,” and even now, that I do sort of grok it, it’s kind of a fluid distinction. Some bands (like Black Sabbath) are clearly heavy metal, some (AC/DC) clearly are not, but I supposed that they’re all hard rock.
I like the AC/DC suggestion. They didn’t spend much time on ballads or nuance.
Yeah, Zeppelin is the group that all the others followed at a great distance.
I know that Cream and the Yardbirds and early Kinks all had elements that Zep built on, but they’re the one who put them together into a sound. As with the Beatles, everything changed after they pointed the way.
All good picks. But I would go with the Who with Keith Moon on drums. They kicked serious ass back in the day when back in the day actually meant a long time ago.
Let’s confuse things a bit by tossing out the first band to use the term “heavy metal,” but were definitely hard rock: Steppenwolf.
Yeah, Sabbath to me is metal, more than “hard rock” but it’s all a continuum. Zeppelin I do think of as hard rock, but they early on were, as I understand it, regarded as metal. And they have a lot of imagery I associate with metal. But their early stuff especially was foundational blues-based hard rock. I also thought of Deep Purple, but they kind of fall into the same category.
I like the Who being in this discussion. That would probably be my #2 choice. But I’ll stick with my off-the-cuff response now that I’ve had time to think about it, as if I had to demonstrate hard rock to an alien who has never heard it before, nobody distills it to its absolute essence like AC/DC’s 3-chord hard rock, with that powerfully, steady, stomping Phil Rudd drumming.
Even though I first mentioned The Who, there’s a case to be made for the answer to this question to be settled by the opening bars of “Back in Black”. I mean, if you needed to give an example of what you mean by “hard rock” to a group of aliens, I’m not sure what else you would need.
It’s funny. That’s exactly the song that’s been ping-ponging in my head since I first opened the thread. 
Can’t understand how I could have forgotten about Bubble Puppy. From 1968. Hard? We’re talking granite.
Another vote for the Who. Or maybe The Who; I’m not sure which is correct.