Director Guillermo del Toro had some specific characters who are close to his heart in mind when he approached Warner Bros. about the Justice League Dark movie.
Del Toro has previously noted that the concept for his film, which was originally given the title Dark Universe, was similar to that of Justice League Dark it was not based on those comics. With Del Toro is no longer attached to the project, a user going by LiteraryBoner asked during an Ask Me Anything session of the movies subreddit of Reddit for some insight into what could have been. Del Toro was diplomatic but did point to certain characters as touchstones.
"It's a WB property, I am not sure I can comment," del Toro replied. "Suffice to say that Demon or Swamp Thing mean to me what Batman and Superman mean to most mortals- perhaps even more."
Del Toro also noted that the love story between Swamp Thing and Abigail Arcane "was a great source of inspiration" for him.
Etrigan the Demon is a Jack Kirby creation dating back to 1972 who made his first appearance in The Demon #1. While the finer details of the Demon's origin story have changed over the years, he remains bound to Jason Blood, a practitioner of the mystical arts with ties to ancient Camelot. Though Etrigan is a rageful Demon, he usually finds himself allied with the heroes of the DC Universe though Jason Blood's machinations. The character was originally based in Gotham City, and so frequently teamed up with Batman.
Swamp Thing was created by Len Wein and Bernie Wrightson and first appeared in House of Secrets #92 in 1971. While never a traditional superhero, the character's nature has changed depending on the era and the writer handling him.
He was originally Dr. Alec Holland, tragically transformed after an experiment gone wrong. Alan Moore famously retconned his origin so that Swamp Thing was not human at all, but a sentient plant-being who represented the "the Green" and its leaders, the Parliament of Trees. In the New 52 era, Scott Snyder blended both origins so that Alec Holland was the avatar of the Green.
The star-crossed love between Swamp Thing and Abigail Arcane, the niece of Swamp Thing's nemesis Dr. Anton Arcane, has been a staple of the character throughout each of these major eras.0comments
While the Demon never joined the Justice League Dark team in the comics, Swamp Thing was a late addition to the original lineup. Both characters were featured in the Justice League Dark animated movie released in February.
The Justice League Dark movie remains in development limbo. Del Toro is no longer attached to direct but was involved as a producer. Doug Liman was attached to direct but Liman left the project in 2016. The film, now officially titled Justice League Dark, is still in some form of development.