The character of Nancy Drew has gone through many permutations over the years. The Nancy Drew Mystery series was revised beginning in 1959; with commentators agreeing that Nancy's character changed significantly from the original Nancy of the books written in the 1930s and 1940s. Observers also often see a difference between the Nancy Drew of the original series, the Nancy of "The Nancy Drew Files", and the Nancy of "Girl Detective" series. Nevertheless, some find no significant difference among the permutations of Nancy Drew, finding Nancy to be simply a good role model for girls. Despite revisions, "What hasn't changed, however, are [Nancy's] basic values, her goals, her humility, and her magical gift for having at least nine lives. For more than six decades, her essence has remained intact." Nancy is a "teen detective queen" who "offers girl readers something more than action-packed adventure: she gives them something original. Convention has it that girls are passive, respectful, and emotional, but with the energy of a girl shot out of a cannon, Nancy bends conventions and acts out every girl's fantasies of power."