Dr. Brenner's return in Stranger Things feels inevitable: could it be revealed in season 4 that he's working for the Russians? Stranger Things has always existed in the shadow of the Cold War; in the real world, the MKUltra Project that inspired the show was an anti-Soviet psyops project. Until Stranger Things season 3, however, that element had been in the background.
The Cold War finally came to Hawkins in Stranger Things season 3, which drew inspiration from all the classic spy thrillers. It revealed a dark conspiracy between the corrupt Mayor Kline and a secret Russian black ops project, which had led to the construction of a sizable Russian lab beneath Starcourt Mall. In Stranger Things season 3, episode 8, Hopper and Joyce successfully infiltrated the base and shut the Russian Gate project down. But they seem to have been too late; the post-credits scene revealed the Russians had extracted biological material from the Upside Down, including at least one Demogorgon.
That post-credits scene clearly sets the Russians up to serve as a major threat in the inevitable Stranger Things season 4. But if the Duffer brothers are going to continue with this Cold War angle, there's one simple question they need to answer: how did the Russians know so much about the Upside Down in the first place? And that's where Dr. Brenner comes in.
The Russians Know Far Too Much About The Upside Down
As noted, in Stranger Things the experiments at Hawkins - which unleashed Eleven's powers and opened the first Gate to the Upside Down - were an offshoot of Project MKUltra. This was a top-secret project launched by the CIA in 1953, with millions of dollars poured into attempts to influence and control the mind. But it's important to remember that it was envisioned as a response to similar experiments being conducted by the USSR; there was a strange sort of "psyops arms race" between the United States and the USSR. In the real world, there's no evidence this ever came to anything, but in Stranger Things it's reasonable to assume both governments were conducting secret experiments that could potentially unlock the Upside Down.
For all that's the case, though, in Stranger Things season 3 the Russians seem to have known far too much about the Upside Down. The show stresses that Hawkins is unique; that when Eleven created the Gate at Hawkins, she damaged the fabric of reality itself. That's why the Russian Gate project moved from the Kamchatka to Indiana - because they realized geography was key to duplicating the effect. But how did they know it was possible to create a portal to the Upside Down in the first place? At Hawkins, a Gate was created by accident in 1983; in the Kamchatka Province, according to Stranger Things season 3, episode 1 the Russians were intentionally attempting to open a Gate just a year later, in 1984.
What's more, there's some evidence the Russians knew what to expect from the Upside Down. In Stranger Things season 3, episode 6, Erica and Dustin discovered cages that were the perfect size to contain a Demogorgon, and electrified cattle prods to force the Demogorgons into them. It can't be a coincidence that they had exactly the right tools on hand to deal with some of the life-forms they'd encounter if they succeeded in opening a Gate. Furthermore, it's clear that the Russians' preparedness paid off, because they did indeed acquire at least one of the creatures.
Why Dr. Brenner Could Be Working For The Russians
The most reasonable explanation is that the Russians somehow got ahold of the research leaked from Hawkins Lab. And, surprisingly, it's possible the culprit is the man who ran Hawkins Lab in the first place, Dr. Brenner. Brenner was introduced in Stranger Things season 1 as Eleven's "Papa," an unethical scientist who had conducted illegal and inhumane experiments upon children like Eleven. In the end, he was believed killed during the Demogorgon's rampage in 1983. In season 2, Eleven learned that Brenner was still alive, but that he'd vanished. For all her efforts, Eleven's "Lost Sister" Kali was unable to track him down.
Stranger Things season 2 generally assumes that the CIA is helping Brenner hide from Kali, but that seems questionable; Kali was able to track down other staff from Hawkins Lab without any difficulty, in spite of the fact they too were under CIA protection. It's reasonable to suggest that something different may have happened to Brenner. Perhaps has defected over to the Russians, and Kali was looking on the wrong continent.
Supporting this argument, notice the timing of the Russian projects and the areas they had knowledge of. Brenner disappeared in 1983, and within just a year the Russians were attempting to create their own Gate to the Upside Down. The Russians were aware that a Gate had been opened at Hawkins, and they knew about Demogorgons; however, there's no evidence they'd made similar preparations for the Demodogs, or had any idea about the Mind Flayer. Those gaps in their knowledge strongly support the notion that their Hawkins mole lost access after Stranger Things season 1. And that fits Dr. Brenner to a T.
Dr. Brenner Could Be The Human Villain Of Stranger Things Season 4
Dr. Brenner is likely to return in Stranger Things season 4; the Duffer brothers have hinted that season 4 may be the end of Stranger Things, which means they'll want to tie up all the loose ends. Eleven's Papa, the twisted scientist at the heart of the Hawkins experiments, is one of the biggest of these. By linking Brenner to the Russians, the Duffer brothers would neatly allow the show to come full circle.
The interesting question, of course, is whether or not Dr. Brenner is a traitor. It's possible he could have been captured by the Russians, perhaps subjected to torture and forced to cooperate with them; indeed, he could conceivably be the American prisoner mentioned in the Stranger Things season 3 post-credits scene. But it frankly seems more probable that he's a willing participant in the Russian experiments, positioned as the face of the Russian project and as the human antagonist of Stranger Things season 4. There'd be a twisted sense of poetry to this; the first season revealed the horrific experiments Brenner had been conducting upon Eleven, and the last season would see Eleven shut Brenner down once and for all. Furthermore, it would also seem poetic for Brenner to be conducting experiments upon captive Demogorgons, given he was almost killed by one of the creatures in Stranger Things season 1.
At the moment, of course, this is just a theory; but it's one that fits the facts, and neatly explains how the Russian threat of Stranger Things season 3 slotted so nearly into the show's overarching mythology. Stranger Things is yet to be officially renewed for season 4, and the first clues will no doubt come from casting; if Matthew Modine is confirmed to return as Dr. Brenner, as is generally expected, then it will make this theory a whole lot more probable.