Kaley Cuoco became a household name due to her role on The Big Bang Theory, but the show also perfectly prepared her for her later role in The Flight Attendant. In The Big Bang Theory season one, Penny is introduced as the vapid neighbor of Leonard and Sheldon. The contrast between the super-intelligent and proudly nerdy roommates and their neighbor serves as the root of The Big Bang Theory's humor, which evolved in later seasons to include other characters. However, it was the character's later evolution and growth that ultimately equipped Cuoco for roles such as Cassie.
As The Big Bang Theory went on, Penny became more layered and interesting, but she always remained the most relatable member of The Big Bang Theory's cast. In her role as a grounding point for the show's more academically-inclined characters, Penny was also, by definition, one of The Big Bang Theory's most complex characters. She was shown to be capable of growth and change, but also slowly revealed that she was often far more emotionally mature than those around her despite her many flaws.
Sitcoms aren't usually celebrated for exploring the depth of their characters. However, over the course of The Big Bang Theory's 12-season run, Penny was given an interesting and rewarding arc that demonstrated Kaley Cuoco's acting talent. The delicate balance of humor and emotional depth was not only a key factor in The Big Bang Theory's popularity, but it actually set Cuoco up perfectly for her Emmy-nominated role in The Flight Attendant. As the titular flight attendant Cassie Bowden, Cuoco played an alcoholic grappling with her own forgotten memories and deep-seated issues in order to prove her innocence in a murder. Not only does she deliver an edge-of-the-seat performance that contributed to The Flight Attendant's positive reviews, but she brought life to the conflicting layers of Cassie's personality that were integral to the show's story. This draws a parallel with Cuoco's role in The Big Bang Theory, with Penny initially being written as vapid and superficial, but slowly revealing more of her character's depth as the show went on.
Cuoco doesn't seem at all out of place leading The Flight Attendant's cast, and that's thanks to the surprising depth she brought to The Big Bang Theory. As Penny, Cuoco was initially playing a one-dimensional girl-next-door role, but over time, her acting talent and criticism of the way the show handled the character led to Penny becoming more interestingly written. This only served to highlight even further how capable Cuoco is at playing characters with hidden depths, something which translated perfectly to her role in HBO Max's comedy-drama mystery thriller.
While it's clear that Cuoco possessed plenty of acting talent even before being cast in The Big Bang Theory, the character development that Penny saw over the show's run allowed her to explore a very specific facet of her acting ability. The same talent was instrumental in bringing The Flight Attendant's Cassie to life, and Cuoco has her most prominent sitcom role to thank. Even after The Big Bang Theory's finale, Young Sheldon continues adding context to Penny's character, proving that Cuoco brought true depth to the role.