Earlier this week, the latest episode of DC's Legends of Tomorrow revealed that the threat following Constantine -- and therefore the season's likely big bad -- was one that sprung almost directly from the pages of a recent run on Constantine: The Hellblazer, to which writer James Tynion IV was a major contributor.
During the run -- which Tynion wrote with Ming Doyle, Riley Rossmo, and Ivan Plascencia -- Constantine had a "serious" boyfriend, and that boyfriend found himself constantly targeted by the forces of darkness...most especially by Neron, the deal-making demon best known as the central antagonist of DC's Underworld Unleashed.
You can see his response below.
Watched the LEGENDS OF TOMORROW ep from last night, and I'm honored that they seem to have taken some inspiration from our run!! I'm also honored that this happened in an episode featuring a murderous muppet, a werewolf, and Marie Laveau!— James Tynion IV (@JamesTheFourth) December 4, 2018
Constantine's ex-boyfriend on Legends might be called Desmond, but he feels like a pretty close adaptation of Oliver, whom John dated during the Tynion/Doyle/Rossmo run. Being close to John made Oliver a frequent target, though -- both himself, and his two daughters (by a previous marriage). Ultimately, he was dragged to hell after a complicated series of deals with demons went bad for him.
Here, the demon Blythe -- who actually claimed Oliver's soul in the comics -- is out of the picture, leaving only Neron. Desmond, also, does not seem to have any children, since Constantine has been charged with his great-great-grandmother with saving "the last of [her] line." In the comics, Oliver lost his soul by dealing with Blythe to save his daughters', whereas on Legends, it seems he lost it by dealing with Neron to save Constantine.
Originally introduced as the main antagonist behind Underworld Unleashed, a miniseries from Mark Waid and Howard Porter, Neron represents the "deal-maker" version of the Devil, and spent most of that story urging heroes and villains to sell him their souls in exchange for increased powers, increased longevity, and other such perks.
The storyline was a useful way for DC to write themselves out of some untenable situations (like Lex Luthor being a convicted felon who had a degenerative clone disease) and to upgrade numerous villains to give them more modern looks and formidable power sets.
In future stories, Neron was usually a little less ambitious, laser-focusing in on a character or group of characters rather than dealing with the whole universe at once.
One notable story was 52, in which he tried to make a deal with Elongated Man to reunite him with his late wife, Sue Dibny. Instead, Ralph conned the con man, eventually binding himself to Neron and then killing himself, essentially trapping Neron's soul in one building for eternity.
...Which, actually, sounds quite a bit like how Constantine got rid of him by sending Desmond to Hell.
After next week's episode, it seems likely that Neron will end up being the big bad of the new season -- something that will fundamentally change the way the Legends interact with the magical castaways they have been chasing down so far.