Dr. Martin Brenner is one of the two main antagonists along with the Demogorgon of the first season of the Netflix original series Stranger Things. He is portrayed by Matthew Modline.
He was a senior research scientist and director of Hawkins National Laboratory. He raised a test subject named Eleven in the lab, testing and pushing the limits of her psychic abilities through various experiments. In one such experiment, Brenner indirectly unleashed a monster from another dimension into Hawkins, allowing Eleven to escape the lab. In the following week, Brenner and his team searched for Eleven while investigating the newly opened gateway to the other dimension.
Most of Brenner's past remains a mystery, expect that he was involved in a controversial project under the codename MKUltra, a CIA-sanctioned research program designed to develop mind-control techniques in which the subject suffered extreme conditions at the hands of the researchers, including use of psychedelic drugs, physical and mental abuse, sleep deprivation, and malnourishment. One of the test subjects was Terry Ives, a pregnant college student, who gave birth to a girl named Jane, who had developed dormant psychic and psychoknetic abilities due to the experimentation on Terry. Brenner and his staff abducted the child, claiming Terry had miscarried, but Terry knew otherwise. She tried to sue Brenner in order to get her daughter back, but failed due to lack of evidence, and eventually entered a lethargic and unresponsive state caused by the trauma and distress of losing her child.
Over the next few years, Brenner raised Jane, now referred to only as "Eleven" (referencing her status as a test subject), in seclusion in Hawkins National Laboratory. Using her youth and lack of social contact to his advantage, he built himself up as a father figure, making her refer to him as "Papa", all the while training and developing her psychological abilities, such as forcing her to crush a Coke can with her mind. On one occasion, he demanded that she kill a cat using her psychokinetic powers, to which she refused. As punishment, Brenner had two members of staff drag the pleading girl to a cell in the lab, but she defeated them, throwing one bodily against the wall and snapping the other's neck. While Eleven sobbed, Brenner picked up up tenderly, considering this new development to be "extraordinary".
Later, Brenner wished to test Eleven's abilities to eavesdrop over long distances. He placed her in a sensory deprivation tank, referred to as a "bath", and she entered a psychic void where she found a Russian agent. Using her powers, she sent the Russian's words back to the lab. However, though the experiment was successful, she also discovered a mysterious creature in the void and became panicked, forcing Brenner to abort the experiment.
Intrigued, Brenner had Eleven placed in the tank again, this time with the goal of making contact with the creature. Eleven succeeded, finding the creature, but in her fear she unintentionally opened an interdimensional rift between the laboratory and the monster's dimension. In the chaos, Eleven escaped the lab through a drainpipe.
Shortly after the Gate's opening, Brenner and a team of scientists went down to the lab's underground subsystem, which had been overrun by otherwordly tendrils and toxic biological growth from the other dimension. He resolved to hunt down Eleven and the Monster, hoping to recover his asset and eliminate the inter-dimensional threat.
The Monster abducted a local boy named Will Byers and takes him into the other dimension. To ensure the secrecy of the lab's illegal experiments and the subsequent incursion, Brenner had the disappearance covered up by placing a fake body in the nearby quarry, employing some Indiana State Police Troopers and a replacement coroner to discover it and ensure that nobody gets too close to it. However, this ruse was found out when Hawkins Police Chief Jim Hopper infiltrated the morgue and performed an unofficial autopsy, discovering cotton stuffing inside the body.
Brenner discovered that Eleven was hiding with Will's friends (Mike Wheeler, Lucas Sinclair and Dustin Henderson), and he and a team of agents left Hawkins Lab to recapture her. However, they were spotted by Lucas, who managed to alert Mike, Eleven and Dustin to their approach. A chase ensued, during which Eleven flipped a government van with her mind, allowing them to escape.
Later, when Jim Hopper and Joyce Byers tried to infiltrate the lab, they are apprehended and brought to Brenner. In exchange for access to the Gate and a chance to save Will, Hopper disclosed that Eleven was located at Hawkins Middle School. Brenner and his agents set off for the school to recapture her. Connie Frazier and a team of agents ambushed her and her friends in a corridor, but she used her biokinetic powers to crush their brains in their skulls, killing them. Brenner held Eleven, who was drained of strength, and attempted to persuade her to return to the lab, but she refused, able to see through his facade as she now understood what love and friendship truly is. The blood of the dead agents drew the Monster through from the Upside Down, and it began slaughtering the agents, allowing Eleven and the boys to escape in the carnage. A horrifed Brenner was subsequently attacked and presumably killed by the Monster, although his fate was left ambiguous.
A newspaper clipping, which had been placed on Hawkin's Police Station's bulletin board by December of 1983, revealed that Joyce alleged that Will was "the subject of a secret government program" run by Hawkins Lab, while a "massive investigation" into "the hidden organization" took place. The article goes on to say that "under legal advise, Brenner has issued no comment" on the allegations. This suggests that either Brenner survived the attack, or that this was a false and libelous statement issued by the lab on his behalf, seeking to present the appearance of normalcy following his death.
In the wake of Brenner's death, it was revealed that Eleven survived her battle with the Monster. She tracked down her biological mother Terry, and communicated with her via telepathy, seeing a younger Brenner taking Eleven - or Jane, her birth name - from Terry immediately after childbirth, and the lies told by Brenner's agents regarding Terry's 'miscarriage'.
Later, Eleven left her mother's house in search of her lost 'sister', who had been a fellow test subject at the lab. She met up with subject 008, now named Kali, who had become a vigilante gang member who uses her power - the ability to induce mental hallucinations - to hunt down and take vengeance on the people responsible for her and her friends' pain and neglect. Eleven, having now retaken the name Jane, accompanied Kali to the home of a former agent of the Department of Energy, and hurt him using telekinesis. Pleading for his life, the agent claimed that Brenner was alive, and that he could tell her his whereabouts. Jane leaves, sparing the agent.
As a reminder of the torture the Lab inflicted on both her and Jane, Kali used her power to conjure a hallucination of Dr Brenner in Jane's mind. However, this was not enough to keep Jane at the gang's side, and after having a vision of Hopper and Mike in danger at the Lab, she leaves Kali and the gang to rescue them. Ultimately, Brenner's true fate is left ambiguous; it is unknown whether the agent's claims were true or false.
In most situations, Brenner is calm, collected and remote, but his quiet and curious nature hides an utterly ruthless personality. He is shown to have little care for human life in his pursuit of scientific progress, willingly keeping a young girl in isolation in Hawkins Laboratory and repeatedly subjecting her to physically and emotionally draining experiments, remorselessly submitting her to cruel psychological torture when she fails or refuses to do so. He acts gently and kindly to Eleven, but in truth the only thing he sees her as is a test subject, and an unstated threat is present in every tender word he says.