I was also wondering who the strange man in the top hat was, that drifted around the stage plunking on an electric guitar.
Since that time, I have come to appreciate Joe Cocker's performance as legendary and inspired. I also learned that the man in the top hat was none other than Leon Russell.
I never knew much about Leon in my younger days. A buddy of mine who was a bit older, was a big fan. I bought a Leon Russell album to try out, and never got much satisfaction from it ( at the time )
Well, thanks to Wikipedia and YouTube...the man, the music and the legend is available for all.
Here are music clips and interviews...plus miscellaneous other Leon footage.
Here's Leon Russell supporting Joe Cocker on his iconic version of "With a Little Help"