Jim Parsons played Sheldon Cooper in every episode of The Big Bang Theory, but he shared this honor with Johnny Galecki (Leonard Hofstadter), Kunal Nayyar (Rajesh Koothrappali), and Simon Helberg (Howard Wolowitz). Parsons' decision to leave the show after 12 years brought about its end, causing some of his colleagues to feel sidelined. Sheldon's character was based on a real-life person, and other characters like Penny, played by Kaley Cuoco, missed out on appearing in every episode. Despite this, Penny became an integral part of the show's fabric and eventually ended up marrying Leonard and having a child, which Cuoco disagreed with.