The hardest piece for piano I ever played (or finished) is the first fugue in Bach's Das Wohltemperierte Klavier. I have played a couple of Chopin's nocturne and when I can add the op.27 no.1 to the repertoire, then I think the fugue will get in second (I got stuck at the second part of the nocturne and today i am completely out of the routine).

I choose Glenn Gould's version as he is the master of Bach. He had a feel for the contrapuntal music that is unsurpassed. (Counterpoint is music where many tunes are played at the same time, creating the harmonics only from the simultaneously played notes (there is probably a more elegant explanation)). Try listening (and see) this clip where he plays Die Kunst der Fuge.

Bach was one of the artists that was forgotten for a long time and then was reinvented, first by the romantic composers and then slowly his oeuvre became part of the general canon. I once was told that Mozart found the Wohltemperierte Klavier in a box of old scores outside an antiquarian and that the fugue began to appear in his music all the time... probably a myth, but Mozart did admire the old Bach. Some of the last pieces that was "reinvented" was the Cello Suites, that was introduced to the public by Pablo Casals in the early 20th century.

To me the cello suites are very familiar as my father plays the cello. They are like the background music of my childhood. Here the second suite is played by the fabulous Danish cellist Morten Zeuthen. I you consider buying a version to stand beside Rostropovich and Casals and the other old masters I would recommend his.

The last Bach I will play for you today is the Goldberg variations. These were also pieces that I listened to as a child. My father told how his uncle, a known jazz musician that had originally been destined to be a concert pianist, but whose career was destroyed by a personal tragedy, played this piece his whole life. In the summer holiday when this uncle visited, my father could hear him play early in the morning. But when my father and his brothers came down, he immediately stopped playing and went to make them breakfast.

I will have to play Glenn Gould again, he made two recordings, one in 1955 and this from 1981. I prefer the mature, late version.

Just to finish this I found this great version of Oscar Peterson playing his tribute to Bach. Peterson was classically educated and as he was a virtuoso already as a teenager he became on of the most technically acclaimed jazz pianists of his time. Here he plays a cadeau to the old master.