One of the biggest lingering questions after Stranger Things season 3 is how the Russians came by the Demogorgon that's shown eating a prisoner during the final episode's end credits. With a summer 2022 release, Stranger Things season 4 will likely be one of Netflix's most highly-anticipated premieres of the year, given the show's popularity thus far and the big things it's been teasing for the latest season. Among these teases is the fact that Jim Hopper has somehow survived and is in a Russian prison, along with a much more dangerous fellow captive: a season 1-style Demogorgon.
Demogorgons have been a central component of Stranger Things since the very first episode, when one stalks and kidnaps Will Byers, setting off all the events of season 1. However, seasons 2 and 3 shift the focus gradually to the bigger, more powerful, and seemingly more intelligent Mind Flayer. Though the Mind Flayer has helped the show in some ways by upping the stakes and dragging more Hawkins residents into the town's ever-growing dark side, Stranger Things' Demogorgons offer a much-needed physical horror that's more clear, immediate, and downright gory than the threat posed by the Mind Flayer. Thus, with all of the new material season 4 claims to be adding, it could actually herald a return to the show's original spooky glory that the Russians are planning something with classic Demogorgons.
But, despite the creature's exciting appearance, there remains a mystery around how exactly the Russians actually obtained their pet Demogorgon. Their plan to open up a new gate to the Upside Down under Starcourt didn't quite pan out in season 3, not to mention the fact that it happened in Hawkins, not Kamchatka Russia. The answer to this question actually lies in one brief, easily overlooked scene during season 3 episode 6, "E Pluribus Unum," while Dustin and Erica are working on rescuing Robin and Steve from the bunker. The Russian experiments in Hawkins in Stranger Things season 3 are set up as one of the season's main plotlines, but very little is actually explained about why they want to open a gate or how the process has been going before the Scoops Troop stumbles onto it. But Erica offers a short glimpse into these mysteries in episode 6 when she notices a big cage near the Starcourt bunker's fuel room and asks Dustin "how big did you say that Demogorgon was?" The pair then move on from this moment rather quickly, but the implication is clear: the Russians have likely captured at least one Demogorgon since they have a cage big enough to fit one.
Unlike the Hawkins lab gate, which was opened by Eleven's powers, Russia's Upside-Down gate in Stranger Things season 3 is the product of advanced machinery. Nevertheless, there's a significant visual parallel between the small rift Eleven opened in season 1 (which grows significantly in season 2), and the partial gate the Russians make in season 3. Thus, just as a Demogorgon was able to slip out of the Upside Down to steal Will in the show's pilot, it's reasonable to expect that one could perform a similar feat through the Russian gate. Presumably, the Russians then captured this Demogorgon in the cage and managed to transport it back to their home turf sometime before, or possibly after, their whole operation in Hawkins went under.
If the Starcourt gate could allow the Mind Flayer's consciousness through, it's plausible that a Demogorgon could manage the same, which is most likely how the Russians have come to have one. The impact of this remains to be seen, however, so hopefully, Stranger Things season 4 addresses Russia's Demogorgon and Hopper's prison escape adequately. The question of how the Russians acquired a Demogorgon and what they plan to do with it is only one small piece of the puzzle Stranger Things season 4 needs to start putting together.