This article contains spoilers for Stranger Things season 4 volume 1.
Stranger Things season 4 finally reveals what happened to Dr. Brenner after season 1. Played by Matthew Modine, Dr. Brenner had a commanding presence in Stranger Things season 1. He was introduced as the man in charge of Hawkins Lab and a ruthless scientist who insisted Eleven (Millie Bobby Brown) call him "Papa" yet also conducted unethical experiments on her as part of his work for the CIA's Project MKUltra program.
Dr. Brenner was initially believed to have been killed by the Demogorgon in Stranger Things season 1, but in season 2 Eleven learned he had survived. A former orderly at Hawkins Lab claimed he could take Eleven and Kali (Linnea Berthelsen) to Brenner, a comment that strongly implied the scientist was still working with the CIA in some capacity. No doubt Kali has spent the last two years looking for him, but Eleven decided she had better things to live for than revenge and committed to her friends and found family instead. Brenner's whereabouts have remained a mystery until Stranger Things season 4.
Related: What Happened Between Stranger Things Season 3 & Season 4
Stranger Things season 4 revealed Brenner not only survived the Demogorgon attack but did so unscathed because he appears to have suffered no serious injuries. He presumably reported everything that happened at Hawkins Lab, including Number One's massacre and the release of the Demogorgon, to his superiors. This probably means Brenner was working with Sam Owens (Paul Reiser), the man who took over Hawkins Lab, all along.
After the events of Stranger Things season 1, the CIA set Dr. Brenner up at a secret lab in the New Mexico desert, in a repurposed storage silo that used to
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