Created by Alan Moore, John Constantine, a roguish magician/detective/conman, first appeared during the author's run on "Swamp Thing" in 1985, receiving his own series, "Hellblazer," under DC's Vertigo imprint in 1988. That book ran for 300 issues before it was relaunched in DC's "New 52" continuity as "Constantine" with a younger take on the antihero.
The Constantine character was also brought to the big screen with a 2005 film directed by Francis Lawrence and starring Keanu Reeves. Guillermo del Toro confirmed last year that he was working on a script based on DC's "Justice League Dark," (tentatively titled Dark Universe) that would include John Constantine as a character. As to how that film winds up being affected by these new televisionplans remains to be seen.
The series joins "Arrow," "The Flash," and "Gotham" as another DC comics-based television series.