I would most certainly agree with Bernhard when he says Bach. Without Bach, no composer would have done what they did. For example, Liszt's chromatisism in the pieces was derived from Bach.
I think Beethoven was a prelude to the Romantic period- being one of the first to show bleak hardship in the music. If it weren't for him, Chopin, Schubert, none of them would have been who they were.
For pianists, Liszt was the groundbreaking factor in musical history. When he invented the piano recital in 1840, and around the time when the keyboard was expanded to 7 octaves..Liszt wrote some of the most virtuosic music ever. The Opera Transcriptions seem to have died out in performance nowadays, but their very existence is a symbol of the piano when it was first tested-when the piano became a limitless power device.
donjuan