The Beatles - Sgt. Pepper's Lonely Heart's Club Band
While you have to give The Beatles credit for a great number of things, the one which is most relevant to this album is the fact that they had a tendency to zag when the public wanted them to zig. Not only would they zag, they would do it so well that zagging would become the only acceptable thing to do.
Sgt. Pepper is as big of a zag as you could ever hope to make. The biggest band in the world got tired of being themselves and reinvented themselves as something different. This is one of the first and most important and influential concept albums. Not only that, it's freaking fantastic to listen to. Oh, and you can really tell that the band has started abusing drugs at this point.