<Li> Cara Buono as Karen Wheeler, mother of teenaged Nancy, middle schooler Mike, and toddler Holly . </Li> <Li> Matthew Modine as Martin Brenner, the scientist in charge of Hawkins Laboratory . He is manipulative and remote . He and his team are searching for Eleven . He reappears in season 2, as he successfully tracks down Eleven </Li> <Li> Noah Schnapp as Will Byers, the younger brother of Jonathan Byers and the son of Joyce Byers . He is captured by a monster from the "Upside Down", an alternate dimension discovered by Hawkins Laboratory scientists . Schnapp was promoted to series regular for the second season, after recurring in the first . </Li> <Li> Sadie Sink as Maxine "Max" Mayfield / "Madmax", Billy's younger stepsister, and a tomboy who catches the attention of both Lucas and Dustin . She ended up being reluctantly accepted into the party by Mike . Sink hoped in the third season she would be accepted by Eleven . </Li>

When did they start to film stranger things