All of which is a long way of saying that both Brainiac and Salvation will likely be issues of concern for the Guardians and, by extension, the Green Lantern Corps. Unlike most space-fairing villains, who just want to conquer the universe because they love power or evil, Brainiac craves information. He travels across the cosmos collecting cities from various planets, shrinking them down and keeping them a collection for study. He’ll take an imposing physical form when necessary, and certainly has ways of fighting with Superman and other heroes, but his primary motivation involves knowledge.
Because Brainiac interferes with many civilizations, he’s exactly the type of threat the Green Lantern Corps exists to fight. Except, here’s the thing: the Corps has rarely fought Brainiac in the comic books. The most notable interaction came in the Panic in the Sky storyline from the 1990s, in which Superman recruited Guy Gardner and others to battle Brainiac, and James Gunn has explicitly said it won’t be an influence on Man of Tomorrow.
Gunn has said the same thing about Salvation Run, the 2008 miniseries that introduced the off-planet prison Salvation. In that miniseries, Amanda Waller and Rick Flag kidnap the supervillains of Earth and send them to Salvation, an uninhabited planet where they will pose no further threat. Of course, the supervillains do pose a threat, eventually forming teams and making it back to Earth.
The season 2 finale of Peacemaker brought Salvation into the DCU, as Rick Flag and ARGUS made plans to send metahumans there, and we know that he’ll eventually do the same with Superman and possibly Luthor. The act of kidnapping people and transporting them to another planet would be enough for the Green Lantern Corps to get involved… if that’s what the Guardians wanted. As Lois Lane in Superman and as Hal reiterates throughout Lanterns, the Guardians are reluctant to contradict local law enforcement. They may consider ARGUS’s actions a matter for Earth’s governments to solve, and forbid the Green Lanterns from interfering.
That may explain John Stewart’s role in Man of Tomorrow. Because he uses an unsanctioned ring, John does not need to follow the Guardians’ rules. If he sees trouble on Earth, then he has the ability to get involved, regardless of the Guardians’ feelings.
The bigger question, then, is how the Guardians will respond to John’s use of an unsanctioned ring, especially if he starts fighting ARGUS. Lanterns doesn’t check back in with Lianna or any of the other Guardians after John’s decision, but we can probably guess that they aren’t thrilled with about a GL who isn’t under their control. Will they send an army to take him down, as Guy threatened? That’s probably not going to happen in a movie that’s mostly about Superman and Lex Luthor, especially not with a cast as stuffed as Man of Tomorrow.
