Dr. Martin Brenner, portrayed by Matthew Modine, is a major character in the first and fourth seasons of Stranger Things. Brenner also makes a cameo appearance in the show's second season.
Brenner, who allegedly worked for the US Department of Energy, was a government figure steeped in mystery and controversy. He was a senior research scientist and director of Hawkins National Laboratory. He had a major role in various controversial experiments, including Project MKUltra. Following MKUltra, Brenner raised a number of test subjects at Hawkins Lab, including Eleven, who possessed psychokinetic abilities.
Brenner tested the limits of Eleven's 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 (informally known as the Upside Down). This culminated in an unsuccessful attempt to capture Eleven at Hawkins Middle School, which drew the attention of the monster. Brenner survived the monster's attack and sustained only minor injuries, but was unable to return Eleven to the lab.
Hawkins Lab was shut down in 1984, and Dr Brenner falsely presumed deceased. By 1986, Brenner and Dr. Sam Owens had established the Nina Project, situated at a top secret facility in the Nevada desert. The project was conceived in response to Eleven losing access to her psychokinetic abilities, and was designed to reactivate her powers via an experimental prodecure. Brenner and Owens wished to use Eleven's abilities to stave off the continued existential threat posed by the Upside Down. After some initial hesitation, Eleven participated and ultimately regained her abilities.
Brenner sought to continue the experiments, wanting to push Eleven's abilities beyond their previous limit. Brenner and Owens began to argue when Eleven insisted on returning to Hawkins, which provoked to Brenner to forcefully incapacitate both Eleven and Owens. Shortly after this, the US Military arrived and commenced a full-scale attack on the facility; General Sullivan believed Eleven to be the root of the issues plaguing Hawkins, and sought to eliminate her. Brenner was fatally wounded in the attack, but Eleven managed to escape unscathed, defeating much of the military in the process. Brenner and Eleven exchanged some final words, and after she departed with her friends, Brenner finally succumbed to his wounds, dying alone in the Nevada desert.
