Where you've seen him before: Astin starred as Mikey Walsh in the '80s classic/Stranger Things touchstone The Goonies. He was the ultimate underdog as the title character in Rudy and was the most loyal of hobbits, Samwise Gamgee, in the Lord of the Rings trilogy.
Who he plays: Bob Newby, a former nerdy high school classmate of Joyce's (Winona Ryder) who starts dating her, much to Hopper's (David Harbour) chagrin. He manages the local Hawkins RadioShack.
Photo Credits: John Paul Filo, CBS; Ron Batzdorff/NBC; George Kraychyk/Hulu; NBC; NBC, Peter Kramer/NBC; Gregg DeGuire/Getty Images; Jason LaVeris, FilmMagic; NBC, Chris Haston / NBC; Chris Haston/NBCU Photo Bank/Getty Images; Vivian Zink/Getty Images; Bill Records/NBC via Getty Images; Gilbert Carrasquillo, FilmMagic; Giovanni Rufino, ABC via Getty Images; Richard Cartwright/ABC via Getty Images; Eike Schroter, ABC