Stranger Things cast transformation from season 1 to 4

Millie Bobby Brown played the role of Eleven / Jane Hopper. A young girl with telepathic and psychokinetic abilities and a limited vocabulary. 

Gaten Matarazzo played the role of Dustin Henderson. The wisecracking friend in the group, Dustin has an outsized personality and confidence to spare. 

Caleb McLaughlin played the role of Lucas Sinclair. Lucas is the steadiest of the group, though he gets easily irked by his younger sister Erica.

Finn Wolfhard played the role of Mike Wheeler. Middle child of Karen and Ted Wheeler, brother of Nancy and Holly, and one of three friends of Will Byers.

Noah Schnapp played the role of Will Byers. The son of Joyce Byers and younger brother of Jonathan Byers.

Natalia Dyer played the role of Nancy Wheeler. Nancy is Mike's older sister and, at the beginning of the show, Steve's girlfriend.

Charlie Heaton played the role of Jonathan Byers. A loner, Jonathan keeps to himself but enjoys photography. He develops a bond with Nancy as they search for his brother and Barb. 

David Harbour played the role of Jim Hopper. Chief of Hawkins Police Department. After his young daughter Sara died of cancer, Hopper divorced and lapsed into alcoholism.

Sadie Sink played the role of Max Mayfield. Billy's younger stepsister, and a tomboy catches the attention of both Lucas and Dustin, eventually choosing Lucas.