Of all the whiz-bang announcements that came out of this year's D23, there was one that proved to be a pretty big head-scratcher: Kit Harington was going to be joining the forthcoming Eternals movie as Dane Whitman, aka Black Knight. It wasn't so much odd that Harington was joining a Marvel Cinematic Universe film—what studio wouldn't want one of the biggest stars to emerge from Game of Thrones?—it was just that the casting left a lot of folks asking, "Wait, the what knight?"

If you were one of those people, you're not alone. Dane Whitman isn't what you'd call well-known, and not entirely essential to the Eternals storyline, either. He's a character that's been around since 1967—he first showed up in Avengers #47, created by Roy Thomas and John Buscema—but never really made a mark. And standing next to the offspring of literal space gods, he's just a guy with a cool sword. But, and this is where casting Jon Snow becomes key, he has one special connection to the Eternals—and it all starts with a character named, coincidentally, Sersi.

The original Black Knight was created by Stan Lee and Joe Maneely for the eponymous comic series The Black Knight, a period story set in the 6th century featuring Sir Percy of Scandia, a formidable fighter who carried the Ebony Blade, a sword made from a meteor and blessed by Merlin that protects its user from harm. In contemporary Marvel comics, however, the Ebony Blade shows up first in the hands of Dane Whitman's uncle, Nathan Garrett, a villain who used the sword to plague the likes of Iron Man and the Avengers. He wasn't great as a bad guy, though; he lasted just a handful of appearances and three years from his 1964 debut in Tales to Astonish #52 before being replaced by his far nicer nephew.

To be blunt, Dane was about as good at being a hero as his uncle was at being a villain. He's a long-time member of the comic book Avengers, but never one of the leading lights—after all, it's hard for a knight to shine next to Thor and Iron Man. Despite all of this, however, his awkward superhero career does have one big highlight: his absolutely ridiculous relationship with the Eternal known as Sersi.

Things started pretty traditionally. Dane and Sersi were both Avengers at the same time, which—according to comic book logic—means that they had to become romantically involved. Unfortunately, this happened at the same time that a villain known as Proctor was driving Sersi to the limits of her sanity; in an attempt to save her mind, another Eternal known as Ikaris bonded Dane and Sersi together in a barely-disguised Pon Farr rip-off known as the "Gann Josin," which linked the two mentally. It didn't take hold, which was a problem for Dane, who by this point had moved his romantic attentions to Sersi's teammate, Crystal. The bigger problem, though, was that the mysterious Proctor was, in fact, Dane Whitman.

OK, sure. Technically, he was a Dane Whitman from an alternate reality who, dumped by his own Sersi, had dedicated his life to traveling through all realities to kill other Sersis, but still. Proctor-Dane was killed by Sersi, which led to both she and regular Dane leaving their reality for convoluted reasons that essentially translated to "We don't know what else to do with them." Dane didn't stay out of the limelight that long; he was back within a year as the leader of Ultraforce, and he'd be back in the regular Marvel Universe again just 11 months later, with the "Gann Josin"—and his relationship with Sersi—seemingly banished to limbo, never to be discussed again.