I'll have a fuller report on this week's comics, including L3W #4, soon. But first, I have some reflections on what Geoff Johns is doing in L3W. Specifically, I believe that Johns is codifying a unified meta-history of the DC Multiverse(s), and putting the Legion squarely in the center of that history.
Earth-Prime is a Special Place
Earth-Prime stands in a unique relationship to all the other Earths, past and present. Earth-Prime is the "real" world, the comic-book version of our world. In Earth-Prime, all the rest of the DC Multiverse (Multiverses?) appears in the pages of comic books. Earth-Prime is the foundation, the "mother universe," the template from which all other Earths are derived.
(Earth-Prime is not the only Earth in which comic books existed: for example, the Flash of Earth-2 appeared in Earth-1 comic books. But Earth-Prime was clearly identified as the world in which the artists, writers, and editors of DC Comics produced the comics that we read.)
Originally, there was a big DC Multiverse with infinite Earths. Then came the Crisis
on Infinite Earths, which ultimately combined all these Earths into one single DC Universe.
From the perspective of Earth-Prime, we-the-readers knew (for example) that Superman's history had been changed, or that Jay Garrick and Barry Allen used to be on two separate Earths. But the characters in those Earths were oblivious to the change: their memories were altered, so they remembered their world as if it had always been the only one.
There were anomalies: Lady Quark, Power Girl, the Pocket Universe, etc. The single universe mutated, changed: there was the Glorithverse, the SW6 batch, various Elseworlds, etc. But still, to the characters in those universes, everything seemed stable. Some people remembered a vague Crisis and a big battle with the Anti-Monitor, but that was it.
Further widescale changes came with Zero Hour. Specifically, there was a completely different Legion (the Legion of Earth-247). Hypertime appeared, then went away and was forgotten.
Then came Infinite Crisis. Earth-247 was destroyed and its Legion left in limbo. A new Multiverse took the stage: instead of an infinite number of different Earths, there were 52.
Through all of these changes, Earth-Prime remained a privileged viewpoint. From the perspective of Earth-Prime, all the previous Earths still existed: they were in the pages of comic books stored in back-issue bins.
The Legion of Earth-Prime
With L3W #4, it's become obvious that the most recent version of the Legion, the "Threeboot" or "Teenage Revolution" Legion, actually hails from Earth-Prime.
In one sense, clues have been there all along. Cosmic Boy had an extensive comic book collection, and various Legionnaires shared his enthusiasm. Often, we saw Legionnaires looking at actual comic books, their covers depicted in such detail that fans could readily identify title and issue number. On what Earth did such comic books exist? Earth-Prime.
We know that Superboy-Prime came from Earth-Prime (so that's where they got his name!). He has all the godlike powers of the pre-Crisis Superman, and he is immune to Kryptonite and magic. (It's been well-established that Kryptonite from one universe doesn't necessarily affect people in another; the Pocket Universe Superboy, for example, was immune to post-Crisis Byrne-era Kryptonite.) Presumably, only Kryptonite from Earth-Prime could affect Superboy-Prime.
Then comes the icing on the cake, in L3W #4: The Threeboot/Teenage Revolution Element Lad creates Kryptonite that affects Superboy-Prime. The Teenage Revolution Element Lad (and hence his whole Legion) is from Earth-Prime. Q.E.D.
Superboy-Prime believes that Earth-Prime was destroyed in the first Crisis, but apparently it wasn't. Or perhaps it got better. And a thousand years later, Earth-Prime produced a Legion of Super-Heroes.
The Time Trapper
We know that the Time Trapper, like Earth-Prime, is somehow "outside" the flow of DC continuity. He doesn't belong to any particular Earth or Multiverse; he transcends them. At the same time, he is somewhat subject to the changes that ripple through continuity; his nature has changed several times in the past 50 years.
Perhaps the Time Trapper himself said it best, around the time of the Legion's 40th anniversary:
I've watched you Legionnaires for a long time, studied you, fought you, even "saved you. I've been both "villain" and "hero" to you. I may even be one of you. I have been, you know. I've tried to control your legacy -- change your history, your origins, your very lives. Anything that didn't quite "fit."
I believed I was helping, but my arrogance caused untold damage, and almost destroyed reality itself.
While all the other characters are trapped in their various continuities, the Time Trapper is on the same plane as the reader: he remembers every change and every intermediate version.
And here's what Johns shows us: the Time Trapper is Superboy-Prime. He is from Earth Prime: our universe, the universe of the editors and writers and artists and readers. Presumably the Time Trapper has the greatest collection of Legion comics ever, and can simply look up any past story he wants.
There's one difference. Superboy-Prime is locked in place. He is a character, with a character's limitations and a character's changeable memory. He exists on the comic book page, in the comic book universe, within the boundaries of panel and page and covers. Sure, he remembers reading comics about Polar Boy and the rest...but he can't get to those comics now. He can't get back to Earth-Prime.
The Time Trapper, though, is beyond those limits. He exists on the comic book page, sure, but he also exists in Earth-Prime. No matter what happens to the Time Trapper within the story, his essence will always exist, and he'll always be back with all the memories he had originally.
I think of it this way. Superboy-Prime is like Batman or Wonder Woman: he is (or has become) a made-up character who exists only on the comic book page. The Time Trapper, however, is like a comic-book version of, say, Geoff Johns: he exists both on the comic book page and in the real world. Anything can happen to the comic book Johns: he could die, gain super-powers, turn into an intelligent octopus, win the Nobel Peace Prize. But none of that would change the real-world Johns.
Come to think of it...the Time Trapper sounds an awful lot like the ultimate comic book writer/editor.
Anybody Remember Zoot Sputnik's Dog?
In the late, lamented 'Mazing Man comic, there was a comic book character named Zoot Sputnik (trust me, it's way complicated). Zoot's dog, Barker, was struck by radiation that gave him "Cosmic Consciousness" -- that is, Barker was able to remember things from one reboot to the next, and ultimately realized that he (along with Zoot and all his friends) was a character in a comic book.
So here's my theory: something happened/heppens to Superboy-Prime that gives him "Cosmic Consciousness." Not only that, but he gains the on-the-page ability to manipulate time and alternate worlds. (Maybe he studies for years on end, like Cosmic Boy did in the "End of an Era" storyline; maybe he gets zapped by something Rip Hunter built; or maybe he gets hired as a writer at DC.) Now he is the Time Trapper.
In a way, the Time Trapper is a symbol of how Legion fans perceive DC management. Both have tried repeatedly to destroy the Legion, both have tried to erase Superman from the Legion's continuity, both have made changes in the Legion...and both have, ultimately, always failed. Because Polar Boy (speaking for all Legion trufans) is right: there will always be a Legion. The fans always force the Time Trapper/DC to bring the Legion back.
So if Superboy-Prime/Time Trapper is DC, and Polar Boy is the fans, then I suppose Geoff Johns is Brainiac 5.
So how will L3W end? How will the Legion defeat Superboy-Prime/the Time Trapper
If I didn't know better, I'd look for the solution to come from the Legion's greatest fan, Flynt Brojj.