Sean Astin (whose "Goonies" is a reference point in "Stranger Things") as Bob Newby, a former nerd who went to high school with Joyce (Winona Ryder) and Hopper (David Harbour). He now manages the local Hawkins RadioShack.
Best known for: "The Goonies" (1985), "Rudy" (1993), and the "Lord of the Rings" trilogy.
Source: Entertainment Weekly
Paul Reiser as Dr. Owens, a high-ranking member within the Department of Energy. He's tasked with containing the events of last year.
Best known for: "My Two Dads" (1987-1990), "Mad About You" (1992-1999), and "Aliens" (1986).
Source: The Hollywood Reporter
Linnea Berthelsen as Roman, a young woman who suffered a big loss as a kid. Though Roman doesn't live in Hawkins, she's somehow connected to the events that occurred at the Department of Energy lab during the first season.
Best known for: From Denmark, she is a newcomer with no major credits.
Source: Variety
Sadie Sink as Max, a tomboy with a complicated history and a healthy amount of skepticism.
Best known for: "American Odyssey" (2015)
Source: Entertainment Weekly
Dacre Montgomery as Billy, Max's older brother, a ladies' man with a violent streak.
Best known for: "Power Rangers" (2017)
Source: ScreenCrush