Hard to pick one band as “the epitome,” but… when I read that post heading, the first thought that popped into my mind was The Kinks (in terms of their early sound, more than for their reputation in music history). The second band (according to sound) that came to mind was The Who.
Certainly, by reputation, The Beatles and the Rolling Stones are more “iconic.”
There’s a lot of good answers. So I’ll just stick to a simple criterion and say that the band that immediately jumped to my mind was Led Zeppelin. I think it’s because when the classic rock format began to appear, all the commercials for the new stations always played the opening guitar lick from Heartbreaker.
I’d go with The Who or Led Zeppelin as the epitome of rock, in the classic sense.
For the Classic Rock radio format, The Eagles or CCR would fit the bill nicely.