I think you are all forgetting Sonny Boy Williamson II - the guy was so influential on the 1960s blues boom. The Yardbirds inc Clapton recorded with him. He also wrote Bring It on Home covered by Led Zep, Eyesight For The Blind covered by The Who, One Way Out covered by the Allman Bros and Your Funeral My Trial covered by John Mayall and many more including Joe!
Of course there were earlier players, but it was Sonny Boy II and Little Walter whose work inspired so many more blues players to have a harp player in their bands. There would never have been a Butterfield or Musselwhite or any of the other guys without them to learn from. Please don't forget the founding fathers!
"The recently formed Edinburgh Blues Club has identified an appetite for the personal communication between musicians and audience that the blues long ago perfected." The Herald Newspaper (Scotland)
http://www.edinburgh-blues.uk