The Beatles stand alone as the singularly most popular and enduring singing group of the twentieth century. Their relation to pop culture and their influence on music and mass culture still grows. Though the band's career ended on sour notes for the individual members, it began with refreshing music, youth-oriented sales promotions, excited fans, and the kind of optimism seldom seen in later years. During the group's heyday, marketers promoted them by producing masses of related merchandise. Some of this material became collectible in the years since its creation. New merchandise still appears in the world market.