To recap, Dr Brenner is the director of Hawkins National Laboratory – and the person responsible for all of the chaos in the first series. At the beginning of his career, he was involved in the CIA-sanctioned Project MKUltra, where test subjects were given drugs in an attempt to foster psychokinetic abilities. Among his victims? Eleven’s mother Terry Ives, who was pregnant during the experiments. When Terry gave birth, Brenner and his cronies abducted Eleven, then named Jane, in order to further develop her “powers”, trying and failing to convince Terry that Jane had been a stillborn – and finally driving her insane.
Years later, while Dr Brenner is forcing Eleven to spy on a Russian agent through her remote viewing capabilities, she ends up puncturing a hole into an alternate dimension – letting the Demogorgon escape into Hawkins and giving Eleven a chance to run away from the lab in the ensuing chaos. In the series finale, Dr Brenner is swallowed whole by the monster while trying to recapture Eleven at Hawkins Middle School – but the question remains whether he’s actually dead or simply on another plane.