This is a question that is as fascinating as it is broad - it depends on a number of variables, the most obvious of which are musical genre, and personal opinion. That said, if we take for example, rock and pop music, you can trace the disparate elements of modern popular music back through a number of influential figures, and this is where taste can overcome objectivity. I'll pin my personal colours to the mast, and let's hope everyone else will want to do the same! For me, although I'm not a huge fan of his music, Bob Dylan has to occupy a major position, and a little further back, pioneers of blues and protest music like Robert Johnson and Woody Guthrie spring to mind. For rock'n'roll Chuck Berry is occupying my own personal top spot, and for guitar pop, The Beatles do it for me. It is a matter of opinion, and people can, and I hope they will, disagree with my selections, and add in their own, so let's see what appears. Thanks for getting the debate started - over to all of you!