- Ascended Fanon: It was speculated by fans that "Brainiac's Daughter" was Brainiac 5 and Supergirl's daughter. In the "Kingdom Come - The 20th Anniversary Deluxe Edition", Alex Ross states he likes that theory, so it is now canon.
Alex Ross: "As silly as it sounds, this character is the combination of two songs by one of my favorite groups, XTC: "That's Really Super, Supergirl" and "Brainiac's Daughter." Apparently people assumed that her origin was from the coupling of old-time Legion lovebirds Brainiac 5 and Supergirl, and so, never having answered this question before myself, I'll go along with this idea. This also suggests that she, like Starman VIII, has traveled back in time from the 30th century."
- Creator Backlash: Mark Waid has expressed regret
in later interviews and statements on how he wrote Wonder Woman in this and its effect on her characterization going forward by later DC writers. - Follow the Leader: Marvel attempted to follow up on this look at a Bad Future where heroes are aged and have children taking up their mantle with Earth X, which also had Alex Ross working on it. Unlike Kingdom Come though, it ended up being much larger in scale and encompassed the entirety of its universe rather than stay focused on a single conflict and Earth X and its sequels were about the origin of everything in the Marvel Universe, as opposed to heroes' legacy as in KC.
- Hostility on the Set: Alex Ross came up with the initial idea and made a 40 page outline for it when he pitched the project, then Mark Waid come on-board and expanded the scope on the story into what it is now. Ross, for his part, was angry that Waid became known as the sole writer and felt he took too much credit. They butted heads frequently, and the comic left them on bad terms.
- Trend Killer: This work is credited with ending the trend of the '90s Anti-Hero by presenting a strong argument against the kind of cynicism and apathy that were rampant in the comic industry at the time. The bright, realistic art by Alex Ross also helped, serving as a stark counterpart to the gritty, stylised drawing styles popularized by people like Rob Liefeld.
- What Could Have Been:
- The original concept, which would have been revealed in the sequel The Kingdom, was that the Kingdom Come universe was actually a revitalized Earth-Two that somehow survived the Crisis. But the idea was later rejected on the fact the Earth-One and Post-Crisis characters wouldn't exist in Earth-Two. If it's true, then they changed their minds so late that they couldn't completely remove that plot thread from the story as The Kingdom is bookended with Superman of Earth-Two pounding on the walls of reality.
- Kingdom Come and The Kingdom both show a great deal of similarity to Twilight of the Superheroes, an idea Alan Moore proposed back in 1987.
- Waid and Ross originally wanted to use Hal Jordan as Green Lantern, but opted to go with Allan Scott to avoid possible editorial interference as Hal was still a villain at that point. Neither one wanted to use Kyle Rayner, the current Green Lantern. A version of Hal would cameo in the follow up JSA arc.
- An early design for Lian Harper featured her modeled more after her mother Cheshire.
- Write Who You Know: Norman McCay is based on Alex Ross' father Clark, right down to sharing his likeness.
