The cinematic efforts of DC Comics under Warner Bros. have been a bit of a mess. The franchise as a whole has been tied quite tightly to a handful of characters, most of whom appear in somewhat unpopular new iterations. The only way to mix things up is to bring new blood like Constantine into the mix. In this case, the new blood is a welcome guest from an earlier age.
Francis Lawrence's 2005 film Constantine enjoyed a fairly impressive financial return at the box office, but critics weren't terribly happy with it. The film was unconnected to any other material, but the long-awaited sequel will likely bring the titular anti-hero into conversation with the rest of the new DCU.
John Constantine was introduced to DC Comics in a 1985 issue of Alan Moore's Swamp Thing. He's an occult detective who brings his mastery of magic to battles with supernatural evil. Moore's concept behind the character imagined a working-class warlock, who would shirk the usual appearance of the wizard. He's known for his signature trench coat, chain-smoking habit, and cynical sense of humor. Keanu Reeves was the first actor to portray the character on the big screen, and he'll be returning to the role in the upcoming sequel. The reintroduction of John Constantine could keep the character safely in his own solo franchise, but he'd be a lot more fun if he were allowed to wander the halls of the wider DCU. Bringing Constantine into the mix opens the door to all manner of mystical elements that could really shake some things up.
In the comics, John Constantine does have a solo series. Hellblazer is one of the longest-running and most popular comic book series in the modern era. It began in 1988, shortly after Constantine's first appearance. The character almost instantly became popular enough to earn a solo project. Hellblazer was generally a bit more grounded than the standard DC Universe. Or, at least the abnormalities were more specific. Characters like Swamp Thing, Zatanna, and Dream from Sandman would pop up, but the Justice League largely stayed out of it. On the other hand, Constantine would occasionally pop up in other series. He was technically reintroduced into the wider DCU in 2011, and he's been a minor figure ever since. This type of integration makes the character a bit more versatile and a lot more interesting.
As it stands, the DCU is very similar in structure to the Marvel Cinematic Universe. It's built around one major superhero team, but most of the founding members have their own cast of supporting characters. There's a second smaller team that rarely crosses over with the headliners, and most of those characters only appear in team-up vehicles. There are only a couple of characters who are likely to appear in multiple chunks of the universe. The lines could be crossed at any time, there are no rules governing the concept, but they are generally obeyed. Constantine offers the start of a new quadrant of the DCU, inhabited by all of his regular collaborators, but it also introduces a ringer who can play with the magical elements of the source material.
Justice League Dark or JLD is a sort-of auxiliary unit of the familiar Justice League. It was introduced to the comics in 2011, just after Constantine rejoined the franchise. The team exists to help battle specifically magical threats that may be beyond the expertise of Superman or Martian Manhunter. The initial line-up included a lot of D-List DC figures like Detective Chimp, Doctor Mist, and the actual Frankenstein's Monster. By the ninth issue of the series, John Constantine became the team's leader and central figure. He was replaced by Zatanna by issue #30, but he remained important. Justice League Dark provides an excellent opportunity for James Gunn to do what he does best. He can take a bunch of his favorite unknown weirdos and turn them into icons, swiftly creating a new list of favorites for every fan. Constantine is the best character to open the door to concepts like the JLD, and Keanu Reeves' take on the character provides the grounding that would make his integration easy and exciting.
The original Constantine is a lot of fun, but it's also a new horizon for the franchise it's about to join. Constantine brought the right mix of horror, action, and intrigue to the big screen. Superhero horror films have been a bit of a mixed bag in recent years, typically because they're struggling against the cinematic universe format and the PG-13 rating. If the new DCU is willing to bring a proper sequel to the 2005 cult hit into its midst, it could change the direction of the franchise. It could also just make a lot of people happy with a long-awaited follow-up. Either way, the working-class warlock is a win-win.