Sadie Elizabeth Sink (born April 16, 2002) is an American actress. She began her career in theater as a child, playing the title role in the musical Annie (2012–2014) and young Elizabeth II in the historical play The Audience (2015) on Broadway. In 2016, she made her film debut in the biographical sports drama Chuck. Sink had her breakthrough portraying Max Mayfield in the Netflix science fiction horror series Stranger Things (2017–2025), and she received critical praise for her performance.

Sink appeared in the horror film trilogy Fear Street in 2021 and starred in Darren Aronofsky's 2022 psychological drama The Whale. She portrays Jean Grey / Phoenix in the Marvel Cinematic Universe, starting with the film Spider-Man: Brand New Day (2026), and will reprise the role in Avengers: Secret Wars (2027) and the untitled X-Men film (2028). She received a Tony Award nomination for Best Actress in a Play for her performance in the Broadway production of John Proctor Is the Villain (2025), and made her West End debut in Robert Icke's production of Romeo and Juliet in 2026.