Which singer left the British pop rock group the Hollies in 1968?

Graham William Nash (born 2 February 1942) is a British-American singer-songwriter and musician. Nash is known for his light tenor voice and for his song writing contributions as a member of the English pop/rock group the Hollies and the folk-rock supergroups Crosby, Stills & Nash and Crosby, Stills, Nash & Young. Nash became an American citizen on 14 August 1978 and holds dual citizenship with the United Kingdom and the United States.

The Hollies are a British pop rock group formed in 1962. One of the leading British groups of the 1960s and into the mid 1970s, they are known for their distinctive three-part vocal harmony style. Allan Clarke and Graham Nash founded the band as a Merseybeat-type music group in Manchester, although some of the band members came from towns further north in East Lancashire. Graham Nash left the group in 1968 to form Crosby, Stills & Nash.