Detective Comics
Detective Comics is an American comic book series published by DC Comics. The first volume, published from 1937 to 2011 (and later continued in 2016), is best known for introducing the superhero Batman in "Detective Comics" #27 (cover dated May 1939).
Batman (Earth-Two)
Batman's origin and history is essentially similar to the Earth-One version of the character, but events unfold in more of a real-time fashion. For example, the Batman makes his debut in 1939, meets Robin, the Joker, Catwoman and Clayface at various points in 1940, the Penguin in 1941, Two-Face in 1942, etc. These dates reflect the publishing dates of the original stories, rather than taking the Earth-One and Modern Age approach of keeping the characters eternally youthful.At the dawn of the Silver Age of comics, DC Comics decided to reintroduce several of their Golden Age superheroes, all of whom had ceased publication several years earlier. Flash and Green Lantern were reimagined as Barry Allen and Hal Jordan. Superman, Wonder Woman and Batman, having been continuously published since their Golden Age introductions, were not given any reimaginings (although much about the mythos of each had evolved slowly over the years). It was later revealed that the current heroes live on a parallel world to the Golden Age heroes: The newer Silver Age heroes are on "Earth-One", while the older Golden Age characters reside on "Earth-Two" (the numbering does not indicate any hierarchy of parallel Earths, only the number by which they were discovered). When Barry Allen met Jay Garrick, it meant there were two Flashes, two Green Lanterns, two Supermen and two Batmen. Unlike the Silver Age versions of the Flash and Green Lantern, who had entirely different secret identities from their Golden Age counterparts, the Batman and Superman of each world were both Bruce Wayne and Clark Kent, respectively. There is no clear demarcation between when the stories of one Batman ends and the other begins. Indeed, many stories from the 1940s and the 1950s were treated as canon to both incarnations of Batman after the concept of Earth-One and Earth-Two was established; Some stories from the mid-1950s could have only occurred on Earth-One, while some stories as late as the early-1960s seem as though they could have also occurred on Earth-Two. DC has mandated that only the Earth-One Batman wore a yellow oval around the bat symbol on his chest, making 1964 the fixed year in which all Batman stories were set on Earth-One, although there are several instances where this is contradicted in-story.