Classic Rock is basically what was Album Oriented Rock (AOR) in the 60s & 70s. So it seems like the Beatles, especially with Sgt. Peppers are the epitome.
But that said, Pink Floyd probably eclipsed them in many way, being much more invested in Album Oriented music.
If you take the other part of Classic Rock to be the Big Arena bands of the 60s & 70s then The Who and Led Zeppelin really step up to the plate.
And though I’m not much of a fan, I would be remiss to not mention The Rolling Stones.