DC Comics is a major American comic book publisher and, alongside its main rival, Marvel Comics, one of 'the big two'. Its primary characters are Batman, Superman and Wonder Woman, but in the 1980s - as a result of its hiring of British and Irish writers like Alan Moore, Neil Gaiman, Grant Morrison, Jamie Delano and Garth Ennis, it began to publish books that were increasingly complex, graphic and infused with adult themes. In 1993 the Vertigo Comics imprint was created to separate these comics (which included Hellblazer and Swamp Thing) from its more child-friendly lines.
In 2011, with superhero comics having become increasingly violent and aimed at mature readers, this rule was relaxed, allowing a DC version of John Constantine to exist in the DC Universe, while the original continued to star in Vertigo's Hellblazer.