Betty Carter was a prominent American jazz singer who was renowned for her improvisational technique and idiosyncratic vocal style. Carter expanded the role of the vocalist in Jazz, to a full, improvising member of the band. Although her voice was not as admired by the public as such vocalists as Sarah Vaughan or Ella Fitzgerald, many consider her to have exercised mastery of the human voice previously unheard in Jazz. Carmen McRae once claimed that "there's really only one jazz singer - only one: Betty Carter."