'Stranger Things' Season 4 theory claims the American is a Hawkins test subject

"Stranger Things" Season 4 is going to reveal the American as a woman and a former test subject from Hawkins Lab, if a fan's theory is to be believed.

The mysterious American mentioned by the Russian soldiers at the end-credits scene of Season 3 is not Chief Jim Hopper (David Harbour) or Dr. Martin Brenner (Matthew Modine). Instead, the prisoner is a female former Hawkins Lab test subject who also has the same powers as Eleven (Millie Bobby Brown).

A fan gave a solid explanation as to why "Stranger Things" Season 4 will reveal another test subject as the American. This involves the gate to the Upside Down that the Russians were able to open in Season 3.

"The American they mentioned has to be one of the other psychics Eleven met in season 2. Think about it: the Americans were only able to open a gate because of El's powers," the fan wrote on Reddit.

The fan pointed out that the beginning of Season 3 made it clear that the Russians had no knowledge of how to open a gate to the Upside Down. Unless there was someone who helped them, someone powerful enough to open the gate.

"They opened their own gate, and the only way they could do it is with one of the psychics. I believe they learned about Eleven's abilities while in Hawkins, and through investigation found the other subjects," the fan continued, adding that this is the only logical explanation why the Russians were able to open the gate. It also gives viewers an idea on the identity of the American captive.

Interestingly, there have been speculations that "Stranger Things" Season 4 will introduce more test subjects from Hawkins Lab. The installment will reportedly bring back Kali, the psychic that El met in Season 2. The past season revealed that there were at least ten subjects who possessed similar powers to Eleven.

Regardless of the fan's theory about the American being a test subject, others are still convinced that Chief Hopper is alive and that he is the American held captive by the Russians. Meanwhile, there are also those that agree with Modine's tease that Dr. Brenner is the American, which would explain why the Russians were able to open the gate to the Upside Down.