Calendar Girl was the criminal moniker of Page Monroe, a former famous fashion model and spokeswoman.
Monroe's transformation into a villain and one of Batman's more colorful opponents was out of wrath and vanity. After her modeling career dried up, she could not find work. Her agent, Irv Kleinman, got her a role in a sitcom, but it did not last long. She vanished from public view and faded into obscurity, surrounded by a rumor of a plastic surgery gone wrong. In reality, she spent that time plotting revenge, gathering resources and fostering a deep seated psychotic obsession with getting revenge on the people and companies/brand names who had turned their backs on her when she turned 30.
She eventually re-emerged as Calendar Girl and proceeded to attack each of her former employers — Gotham Motors, Donna Day Fashions, and WGB Network on the anniversary of her contract expirations. Each contract expired during a different season and she dressed in a themed costume for each occasion, with her attacks having a similar theme. Like many of the Batman villains, she was accompanied by underlings who dressed and behaved in a unified manner; in Calendar Girl's case her henchmen were shirtless attractive men who wore bow ties and tuxedo trousers. Calendar Girl was based out of an old nightclub she owned called Faces.
Her plans for revenge were thwarted by Batman and his team. She was later arrested by Harvey Bullock, who bluntly tore off her mask to see Monroe's true face, and she screamed in shame and broke down in tears while hiding her face. Under her mask, she was revealed to still be very attractive, but could only see her imperfections now.
Calendar Girl appears to suffer from a psychological condition classified as body dysmorphic disorder, an obsession with one's own physical appearance and an insistence on seeing oneself as flawed or ugly, despite all evidence to the contrary. Actress Audrey Hepburn was rumored to suffer from this disorder: despite being acclaimed as one of the most beautiful women of her day (arguably, of all time), she could not help but see herself as ugly.
Calendar Girl was voiced by Sela Ward, an actress who, like her animated counterpart, is celebrated for having retained her beauty through the present day. At the time the episode of The New Batman Adventures was produced, Ward was conducting a campaign of protest against ageist bias in Hollywood, and later she produced a documentary depicting Hollywood's obsession with youth and its harmful effects on public perception. Her appearance in this episode could be construed as part of the same campaign. Like her voice actress, Calendar Girl had long dark hair.
Her character is similar in name to Calendar Man (Julian Gregory Day), one of Batman's rogues from the comics. While Calendar Man is obsessed with committing his crimes in connection with particular days of the year, while Calendar Girl's criminal identity is obsessed with her age. The sole similarity with the two villains was dress: Calendar Man often dressed in the custom connected to the day of the crime, while Calendar Girl sometimes wore outfits connected to the season, such as an Uncle Sam hat when she committed her summer crime (reflecting the 4th of July). Her civilian name may be derived from Bettie Page and Marilyn Monroe, two famous pin-up girls.