With the release of Spider-Man: Brand New Day, Marvel Studios has officially introduced one of Marvel Comics’ most iconic mutants to the Marvel Cinematic Universe (MCU): Jean Grey, played by Stranger Things actor Sadie Sink. ‘Spider-Man: Brand New Day’ FIRST Reactions: Early Reviews Call Tom Holland’s Next Spidey Tale a Mini ‘Avengers’-Level Hit. Who is Jean Grey in X-Men and Marvel ComicsCreated by writer Stan Lee and artist Jack Kirby, Jean Grey made her debut in The X-Men #1 in September 1963. Sadie Sink on Her Casting in ‘Spider-Man: Brand New Day’Sadie Sink’s inclusion in Spider-Man: Brand New Day was kept strictly under wraps for over a year. ‘Spider-Man: Brand New Day’: Sadie Sink Reveals ‘Stranger Things’ Cast Knew About Her Secret MCU Role (Watch Video).