In early March 2017, Iain Armitage was cast as the younger Sheldon, and Zoe Perry as his mother, Mary Cooper. Perry is the real-life daughter of Laurie Metcalf, who portrays Mary Cooper on The Big Bang Theory. Lance Barber stars as George Cooper Sr., Sheldon's father; he had previously appeared in one episode of The Big Bang Theory. Raegan Revord stars as Missy Cooper, Sheldon's twin sister; Revord only got the part after repeatedly asking her mother to be allowed to read for the role. The show also stars Montana Jordan as George Cooper Jr., Sheldon's older brother. Jim Parsons reprises his role as adult Sheldon Cooper, as narrator for the series. In July 2017, Annie Potts was cast as Meemaw, Sheldon's grandmother. In March 2024, it was announced that Jim Parsons and Mayim Bialik will guest star on the series finale as their original characters from The Big Bang Theory.