9. Bernadette Rostenkowski (Melissa Rauch)
"Gosh, Amy. I'm sensing a little hostility. Is it maybe because like Sheldon's work, your sex life is also theoretical?" Until season three, Bernadette was a supporting character introduced as a waitress friend of Penny's, studying microbiology, with the unfortunate luck to be set up with Howard. As the relationship grew, so did the character and Rauch was credited as main cast from then on. Though Bernadette isn't the most exciting or hilarious character on the show, she still deserves a place on the list, because she's a necessary character. Even if it is just for putting up with her fictional husband or helping balance the friendship between Penny and Amy.