William Keith Relf (22 March 1943 – 14 May 1976) was an English musician, best known as the lead vocalist and harmonica player for The Yardbirds. 　　Relf started playing in bands around the summer of 1956 as a singer, guitarist, and harmonica player. Despite his suffering from respiratory problems,his blues harp was a key part of the Yardbirds' sound and success, according to many, and his vocals may have been as important a contribution to the band,as that of their three lead guitarists Eric Clapton, Jeff Beck, and Jimmy Page - who were augmented by bassist Paul Samwell-Smith, guitarist/bassist Chris Dreja, and drummer Jim McCarty. 　　Relf co-wrote many of the original Yardbirds songs ("Shapes of Things", "I Ain't Done Wrong", "Over Under Sideways Down", "Happenings Ten Years Time Ago"), later showing a leaning towards acoustic/folk music as the sixties unfolded ("Only the Black Rose").He also sang an early version of "Dazed and Confused" in live Yardbirds concerts, a song later recorded by the band's successor group Led Zeppelin.