John Constantine, Hellblazer is an American contemporary horror comic-book series published by DC Comics since January 1988, and subsequently by its Vertigo imprint since March 1993, when the imprint was introduced. Its central character is the streetwise English sorcerer and con man John Constantine, who was created by Alan Moore and Stephen R. Bissette, and first appeared as a supporting character in Swamp Thing (vol. 2) #37 (June 1985), during that creative team's run on that title. Hellblazer was released as launch title for Vertigo in March 1993, becoming the imprint's longest-running series and the only launch title to continue its run into the new century. In 2013, the series concluded with issue 300, and was replaced by Constantine, which returned the character to the mainstream DC Universe. The original series was revived in November 2019 for twenty-four issues as part of The Sandman Universe line of comics, under the DC Black Label brand. Well known for its extremely pessimistic tone and social/political commentary, the series has spawned a film adaptation, television show, novels, and multiple spin-offs and crossovers.

The series was the longest-running and one of the most successful titles of DC's Vertigo imprint, and was the stepping stone for many British writers. Notable writers who have contributed to the series include Jamie Delano, Garth Ennis, Eddie Campbell, Paul Jenkins, Warren Ellis, Grant Morrison, Neil Gaiman, Brian Azzarello, Mike Carey, Denise Mina, Andy Diggle, and Peter Milligan. Hellblazer was one of the first modern occult detective fiction works and heavily influenced the genre to come.^{[citation needed]}

After favorable reader reaction to John Constantine's appearances in the comic-book series Swamp Thing, where he had been introduced by writer Alan Moore, the character was given his own comic-book series in 1988. The series was intended to bear the title Hellraiser, but this title was revised before publication due to the contemporaneous release of Clive Barker's unrelated film of the same name. Initial writer Jamie Delano was, in his own words, "fairly ambivalent" about the change of title.

The initial creative team was Delano and artist John Ridgway, with Dave McKean supplying distinctive painted and collage covers. Delano introduced a political aspect to the character, about which he stated: "...generally I was interested in commenting on 1980s Britain. That was where I was living, it was shit, and I wanted to tell everybody." The book, originally published as a regular DC Comics title, became a Vertigo title with the imprint's launch in March 1993 (issue #63 of the series). In October 2011, it was announced that this would join DC titles in being published digitally on the same day as its physical release, starting in January 2012.

Many writers after Delano's foundational run had lengthy runs on the series, such as Garth Ennis and Mike Carey, who respectively had the second- and third-longest runs on the book (only behind Peter Milligan). Other writers who wrote for the series include Paul Jenkins, Warren Ellis, Brian Azzarello, Neil Gaiman, Grant Morrison, Denise Mina, and Andy Diggle.

Numerous artists worked on the series, as well, such as John Ridgway (the original series artist), Simon Bisley, Mark Buckingham, Richard Corben, Steve Dillon, Marcelo Frusin, Jock, David Lloyd, Leonardo Manco, and Sean Phillips. Cover artists included Dave McKean (who designed the first run of the series' covers), Tim Bradstreet (who designed the most), Glenn Fabry, Kent Williams, David Lloyd, and Sean Phillips.

Hellblazer was set in a contemporary world, albeit a world of magic and supernatural conflict behind the scenes. Although the official setting of the series was the DC Universe, well-known DC characters were rarely seen or mentioned. Some DC Comics characters – most notably the fringe supernatural characters such as Zatanna, the Phantom Stranger, Shade, the Changing Man, Dream of the Endless, and the Swamp Thing – made appearances.

John Constantine, the main character of Hellblazer, was portrayed as a kind of confidence man and occult detective who did morally questionable things, arguably for the greater good. He usually triumphed through guile, deceit, and misdirection, but often made more enemies in the process than he defeated. Indeed, it was a common theme in the book that Constantine was unable to effect any lasting change or enjoy unequivocal victories. While sometimes striving for the good of mankind, Constantine was often manipulative and a dangerous person to have as a friend, as the lives and souls of those around him became perilously involved in his misadventures. He took pains to protect himself from direct attacks, but his friends and relatives were often endangered in order to strike at him. The spirits of deceased friends haunted him, individually or as an entourage of ghosts.