Winona Ryder as Joyce Byers, the mother of Will and Jonathan Byers.

David Harbour as Jim Hopper, chief of Hawkins Police Department. 

Finn Wolfhard as Mike Wheeler, middle child of Karen and Ted Wheeler, brother of Nancy and Holly.

Millie Bobby Brown as Eleven / Jane Hopper ("El"), a teen girl with telepathic and psychokinetic abilities.

Gaten Matarazzo as Dustin Henderson, one of Will Byers' friends.

Caleb McLaughlin as Lucas Sinclair, one of Will's friends. 

Natalia Dyer as Nancy Wheeler, daughter of Karen and Ted and older sister of Mike and Holly. 

Charlie Heaton as Jonathan Byers, the older brother of Will Byers and the son of Joyce Byers.

Cara Buono as Karen Wheeler, mother of Nancy, Mike, and toddler Holly. Karen has a brief fling with Billy in season 3.

Matthew Modine as Martin Brenner, the scientist in charge of Hawkins Laboratory and training Eleven.

Noah Schnapp as Will Byers , the son of Joyce Byers and younger brother of Jonathan Byers.

Sadie Sink as Max Mayfield, Billy's younger stepsister, and a tomboy who catches the attention of both Lucas and Dustin, eventually dating Lucas. 

Joe Keery as Steve Harrington, a popular high school student and the boyfriend of Nancy Wheeler.

Dacre Montgomery as Billy Hargrove , Max's violent, unpredictable, and abusive older stepbrother. In season 3, he is controlled by the Mind Flayer and later sacrifices himself to protect the kids.

Sean Astin as Bob Newby, a former schoolmate of Joyce and Hopper who runs the Hawkins RadioShack and is Joyce's boyfriend, putting him at odds with Hopper.

Paul Reiser as Sam Owens, a Department of Energy executive who replaces Brenner as director of Hawkins Laboratory.

Maya Hawke as Robin Buckley, a girl who works alongside Steve at the ice cream store in the mall who later comes out as a lesbian.

Priah Ferguson as Erica Sinclair, Lucas's 10-year-old sister who helps the group.

Brett Gelman as Murray Bauman, a conspiracy theorist, private investigator, and longtime friend of Hopper's.

Jamie Campbell Bower as Henry Creel / One / Vecna, a murderous psychic being from the Upside Down revealed to have created the Mind Flayer.