WARNING: The following contains minor spoilers for Batman: The Long Halloween Special #1, on sale now from DC Comics.
The Calendar Man first appeared in Detective Comics #259, by Bill Finger and Sheldon Moldoff, as a petty crook who took out an ad in The Gotham Gazette entitled "Calendar Man Challenges Batman." As a minor criminal whose crimes never amounted to much and whose devotion to themes surrounding days and dates often led to clues that resulted in his apprehension, he is almost always presented as more of a menial caricature than a worthy opponent of the Dark Knight.
During the events of Jeph Loeb and Tim Sale's highly acclaimed The Long Halloween and its sequel Dark Victory, both written by Jeph Loeb and penciled by Tim Sale, the vantage of the character from his cell in Arkham showcases less of the flamboyant burglar and more of the small man plagued by petty jealousies.
The Long Halloween takes place over the course of a year, early in the annals of Bruce Wayne returning to Gotham after honing the skills that he would eventually use to become the scourge of the underworld. Chief among those in the criminal hierarchy was Carmen "The Roman" Falcone, the head of an organized crime syndicate whose wealth, resources and muscle made him almost untouchable. When members of his family or those loosely associated with his illegal enterprises start showing up dead on holidays over the course of months, Batman and the police start looking for a serial killer the press had to come to call, Holiday.
Each step of the hunt presents new suspects and avenues of exploration as Catwoman seems intricately involved in some capacity as she shadows Batman across the city while he pursues shadows and false leads. The Dark Knight rogues gallery is on display, with the Mad Hatter, to the Joker, Scarecrow, Poison Ivy and other prominent Gotham villains wreaking havoc as Batman tries to put the pieces of the puzzle together and eliminate false positives. While Arkham Asylum is as much of a turnstile as ever, the Calendar Man never manages to escape and plays the role of Hannibal to Batman's Clarice.
Calendar Man offers up his niche expertise to a clearly desperate crimefighter who isn't quite yet the world's greatest detective that he'll become. Julian Gregory Day, the Calendar Man's documented identity, seems to cooperate out of a need to be remembered. Holiday's murders are overshadowing his string of thefts, both orbiting the prominence of days of the week as central to their thematic impact.
Day watches as the sociopaths who have made a name for themselves in the streets of Gotham shed Arkham like a husk, all the while the memory of his deeds continue to fade. Dark Victory takes place a few months after the events of The Long Halloween conclude. Harvey Dent's replacement in the D.A.'s office is determined to set aside Holiday's conviction, a new serial killer called the Hangman in lynching cops and Dick Grayson comes into Bruce Wayne's life.
Another round of releases from Arkham occur, but this time the Calendar Man also manages to escape and uses the opportunity to infiltrate Holiday's home and attempts to convince him to commit suicide by pretending to be the disembodied voice of his dead father. The ploy doesn't work and Calendar Man is beaten within an inch of his life for the ruse, used by Two-Face in a twisted scheme. This attack likely also played into the Calendar Man's recent attack on Two-Face and his wife Gilda Dent, the other Holiday Killer, in Loeb and Sale's Batman: The Long Halloween Special, which takes place after both previous series.
Over the course of The Long Halloween and its sequels, Calendar Man was treated with the same seriousness as Gotham's A-list villains, despite his history. However, the step from robberies to murder also denotes just how vacant his own sense of self had become.