In what might turn out to be a very important piece of exposition, tonight's episode of DC's Legends of Tomorrow name-dropped one of DC's most powerful supernatural villains.

At the same time, comic book fans have likely begun to suspect that John Constantine's story is drawing from 2015's Constantine: The Hellblazer by James Tynion IV, Ming Doyle, and company.

That run, which took place shortly before the Rebirth relaunch, featured a reinvented version of Neron, but also was the first time that John Constantine's bisexuality was a story factor within the DC Universe.

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/Riley Rossmo run. Being close to John made Oliver a frequent target, though, and both he 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.

Tynion was pretty pleased to hear that they were using elements of his story, it seems...

IT IS KILLING ME THAT I AM NOT ALREADY WATCHING THIS //t.co/mM7EATeJKx — James Tynion IV (@JamesTheFourth) December 4, 2018

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.

But who is Neron?

Well, he got briefly name-dropped this episode, but has a larger role in DC's history than almost any villain the Legends have faced yet.

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.

DC's Legends of Tomorrow airs on Monday nights at 9 p.m. ET/PT, following episodes of Arrow on The CW.