Few figures in 20th century American music had as pervasive an influence as David Crosby. As a founding member of the Byrds, he shaped the ringing sound of 1960s folk-rock and pioneered trippy psychedelia, yet his greatest fame came as part of Crosby, Stills & Nash, a supergroup he formed with Stephen Stills and Graham Nash that helped usher in the mature, reflective '70s.