During The Sandman reveal and panel at Netflix Geeked, creator Neil Gaiman & Jenna Coleman officially revealed that her character Johanna Constantine was in fact a replacement for John Constantine. In the comics, Johanna Constantine was an ancestor of John Constantine who lived in the 18th Century and became an occasional ally and foil for Morpheus. So far there has been no mention or stills of that Constantine, at least not in season one so far. For now, this show's Constantine exists firmly in the 21st Century.
Gaiman and showrunner Allan Heinberg described Coleman's Johanna Constantine as "powered up" with a more expensive white trenchcoat rather than the filthy, faded raincoat that has been John Constantine's signature look. She's also a bit "posh", with a higher class of clientele for her magical services, including the Queen and the Royal Family, but still the same "heartbroken, wounded, bitter" magician with a conscience that we all know from the comics.
John Constantine only appeared in one issue of The Sandman comic, and Johanna Constantine appears in two later in the run. The first time she meets Morpheus is when she's hunting the Wandering Jew in her quest for the secrets of immortality, and the second time is when Morpheus makes a deal with her to go on a mission in Revolutionary France. Johanna Constantine and Rose Walker (Vanesu Samunyai) will play pivotal roles in Morpheus' (Tom Sturridge) arc in season one of The Sandman show, which suggests that Constantine will be appearing in quite a lot of it. The trailer already suggests the change from the comics where Johanna Constantine meets the long-lived Mad Hettie who tells her that the Dream King was coming back. That Constantine didn't know that Morpheus was more than a myth and fairy tale already means Johanna Constantine is this story's version of John Constantine, not an immortal Johanna Constantine who's been around for over 200 years.
That tease of a scene is how every Hellblazer story usually starts: Constantine hears from a source that someone or something is at large, and Constantine investigates. That's an encouraging sign. Coleman also plays Constantine with a Cockney accent (with a bit of her native Hull slipping out) as well, another encouraging sign. She also displays the cocky swagger we know from Constantine that hides any fear or worry lurking underneath.
As panel host Felicia Day said, there's going to be a lot of Johanna Constantine cosplay. Her look was surely designed knowing that would happen: an elegant dark suit and tie with a stylish white trenchcoat as opposed to the rumpled suit and tie under the faded dirty raincoat of the male Constantine. It's a new, fresh take after more than 37 years of the rumpled Cockney bloke.
If you want the old Constantine, you can always revisit Matt Ryan in the one-season Constantine series and Legends of Tomorrow as well as the comics. It's interesting to note that Ryan played Constantine with the character's native Liverpool accent (with his normal Welsh sometimes slipping out) that Jamie Delano wrote in the comics. Delano introduced Constantine's origin of being Liverpool-born before making London his home base as an adult. Constantine's creator Alan Moore wrote Constantine with the first authentic Cockney character's voice in American comics back in 1985. In The Sandman, Coleman will actually be playing Constantine as Cockney on TV for the first time. The Sandman premieres on Netflix on August 5th.