Sadly most people nowadays will only have heard of the "I believe in Father Christmas" tune (accompanied with the strange desert video).
My first intro to Greg Lake (and prog' rock) was when I was a kid in music class. The Teacher used to play the LP Pictures at an Exhibition by ELP during class. I thought that this was amazing, as the music built up so many images, and helped to set the scene. I can still imagine The Gnome scurrying around everytime I hear that piece of music. Classic album.
RIP Greg Lake.