Crosby, Stills & Nash (CSN) is a folk rock supergroup made up of David Crosby, Stephen Stills and Graham Nash, also known as Crosby, Stills, Nash & Young (CSNY) when joined by occasional fourth member Neil Young. They are noted for their intricate vocal harmonies (similar to Simon & Garfunkel), often tumultuous interpersonal relationships, political activism, and lasting influence on American music and culture. All four members of CSNY have been inducted into the Rock and Roll Hall of Fame twice, though Young's multiple inductions were for work not involving the group. Prior to the formation of CSN, each member of the band had belonged to another prominent group. David Crosby had performed rhythm guitar and vocals with folk-rock group The Byrds; Stephen Stills had been a guitarist, vocalist and songwriter in the band Buffalo Springfield; and Graham Nash had been a guitarist, vocalist and songwriter with The Hollies, one of the 'British Invasion' acts.