Behind the laughs and science-filled banter of The Big Bang Theory lies a cast full of brilliant and fascinating women. While the series gave us unforgettable characters like Penny, Amy, and Bernadette, the real-life women who portrayed them have some surprising secrets fans may not know.

Kaley Cuoco (Penny) wasn’t originally cast in the pilot. The first version of the show featured a different female lead named Katie, who was played by Amanda Walsh. It wasn’t until a reworking of the pilot that Kaley landed the role of Penny—and the rest is sitcom history. Kaley is also a trained equestrian and often credits horseback riding as her escape from Hollywood pressure.

Mayim Bialik (Amy) is not just playing a scientist—she actually is one. Mayim holds a Ph.D. in neuroscience from UCLA, making her one of the few actors to portray a character with a degree she genuinely earned. Her deep understanding of science even helped the writers maintain some accuracy in Amy’s dialogue.

Melissa Rauch (Bernadette) surprised many fans with her signature high-pitched voice on the show—it’s not her real speaking voice! In interviews, she’s shared that the voice was inspired by her own mother’s tone, exaggerated for comedic effect.

Off-screen, these women have built impressive careers and embraced causes close to their hearts. From activism to voice work and producing, the women of The Big Bang Theory continue to impress far beyond the world of nerdy roommates and physics jokes.