Several people have laid claim to the slogan: Wikipedia notes that American ‘cultural critic’, and folklorist the late Gershon Legman has laid claim to it but there is little corroborating evidence. A more substantial claim was made by one Diane Newell Meyer who was a student at the University of Oregon in 1965, the year in which the slogan first appeared.
Creative Review has carried out an extensive investigation into who was responsible for its creation.
Click the image to read the piece.