Never again let Gen Xers tell you they are underserved, culture-wise. Sunday night’s TV slate proves they ain’t. That evening features not just one hour of a series derived from a transformational superhero comic book of the 1980s— Watchmen, on HBO—but two. Because Sunday is also the beginning of the CW’s Crisis on Infinite Earths.

On TV, Crisis will be a five-hour crossover from what’s generally called the Arrowverse. Arrow was the font, a show about the DC Comics hero Green Arrow, from which spewed The Flash and Legends of Tomorrow. Also in the ‘verse are Supergirl, which started on CBS and switched to Arrow’s home on the CW, as well as Batwoman and Black Lightning. As in the comics, superheroes live in multiple separate universes but can visit each other in times of great need, like when ratings are down or during a holiday hiatus.

It’s a lot to process, right? So was the original comic. Stan Lee and his fellow creators at Marvel Comics rightly get a lot of credit for squeezing all their books into a shared narrative space. But the pioneer was the 1961 book “The Flash of Two Worlds,” when the speedster hero Flash met his Golden-Age antecedent, who had not been “canceled” so much as “was living in another universe.” Team-ups are cool—that’s what books like Justice League or Avengers are for, getting more kraka-thoom for your buck. But the storytelling implication of “Two Worlds” and the subsequent annual crossovers between 1940s heroes on Earth-2 and present day heroes on Earth-1 is both awesome and terrifying: Those entire canons take place in a giant multiverse—one giant story with a nominally plausible continuity.

By the 1980s DC Comics’ bosses feared that their internal continuity had grown multifariously opaque to new readers. Multiple versions of heroes were having adventures in multiple timelines on multiple Earths. (We are on Earth Prime, by the way—a world with, if you can believe it, no costumed vigilante superheroes except in so-called “comic books.”) Heroes from other companies that DC had acquired, like Captain Marvel from Fawcett, lived in their own universes. The accumulated story cruft of four decades slowed the whole endeavor down, like barnacles on a hull.

So popular DC writer Marv Wolfman pitched a way to clean it all up. Over years, a bad guy would destroy most of these alternate comic universes, and after lots of big fights, the rest would merge into one single universe, one storyline, with one new past and present. Some characters—notably Flash and Supergirl—would die. Others would have their origins and backstories retroactively changed in continuity, or retconned. “The idea was, this gigantic story was going to be considered as one gigantic story, not as 40 different stories with an overlapping setting, and the big story was going to change drastically,” says the comics historian and critic Douglas Wolk. “And it kind of did. Crisis became an inflection point in this enormous story that had been going on for decades and decades that was supposed to simplify everything. Of course it actually complicated everything.”

Subsequent writers played their usual game of Exquisite Corpse, adding to or revising the new rules. Multiple universes came back, dropped away, came back again. Other, later crises—Final Crisis, Infinite Crisis—got even weirder and more cris-tastic.

But narrative aside, along with Watchmen and The Dark Knight Returns (and to a somewhat lesser extent the Marvel crossover Secret Wars), Crisis was one of the late-1980s books that changed comic book storytelling. Crisis was the first “maxiseries,” a year-long series that pulled in nearly every ongoing title from DC Comics. That’s good for sales, and its popularity made complicated crossover events into regular occurrences—with greater or lesser consequences for the Big Story, and for the business around it.