u/papiforyou

I'm trying to understand what's going on here, and the history of it. I understand that if you tune a piano to a perfect C major scale with just temperament, it will sound more in tune to the natural ratios, but would be impossible to play every other key on (G# for instance). Equal temperament places every key slightly out of tune, but allows you to play any key you want relatively in-tune.

Was Bach's "Well Tempered Clavier" the first major collection of music to be written in equal temperament? If so, was Bach trying to say that each key, with this new system, has its own "character"? As opposed to just tuning, in which he thought that each key was the same and didn't have a distinct character?