Keith Jarrett is a jazz piano player who has crossed over to a level of fandom exclusive to a very few musicians in the world, regardless of their styles. If you're reading this, you've probably heard him, as a soloist, with his trio, maybe even in his early days with Miles Davis or Charles Lloyd.
However, it may also be that you've never heard him playing a Gershwin tune in a stride-piano vein (the first two and a half minutes in the following video).
In the comments on the YouTube page, some seem not to believe that this is indeed Jarrett. However, Norwegian musician Per Husby says this about the video:
I can confirm that the clip is actually Jarrett. The original tape now resides in the Norwegian Jazz Archives as part of the Randi Hultin collection, donated to the archives after her passing away.
However, the info regarding the actual recording is incorrect. The quartet part (the track is cross-faded into a concert version of Forest Flower by the quartet) may well have been recorded at the Oslo concert on May 7, 1966, but Jarrett played no solo performance, Tatum-style then (I know, I was in the audience). However, the day after, the quartet was invited to Randi Hultin's house to celebrate Jarrett's birthday, and on that occasion Jarrett sat down at Randi's piano and played several solo pieces, some of which was recorded by Randi on her home tape machine. (If you listen closely, I think you might hear Randi and Lloyd chuckling in the background a couple of places while he is playing). The whole recording is about 10 minutes long - so the YouTube thing is just a small excerpt. God knows where they got this clip from, though - they most certainly did not get it from Norwegian Jazz Archives.