While the DC Universe has always been home to a plethora of dark and demonic entities, the heroes who have been tasked with defeating these monstrosities tend to look the part. That couldn't be farther from the truth when it comes to DC's premiere supernatural antihero, however, as John Constantine would be the most unassuming figure if he hadn't made his own look so iconic. That said, even the Hellblazer himself has had his fair share of competition over the years, including a couple of fellow mages who were tailor-made specifically to replace him.
Source:https://www.cbr.com/dc-replaced-darkest-hero-twice-where-are-hellblazer-stand-ins/