Missy Cooper, Sheldon's twin sister, became a fan favorite side character despite only appearing twice in The Big Bang Theory. However, the release of Young Sheldon provided more insight into Missy's personality and showed her as arguably the most well-adjusted member of the Cooper family. The show also established Missy's growing resentment toward her mother for favoring Sheldon and explained her rebellious phase seen in TBBT season 6 finale. These changes make fans see her differently and suggest a potential spinoff to explore her character further.