Leonard's Sister

This unnamed woman is the eldest child and only daughter of Mr. Hofstadter and Beverly Hofstadter, as well as the sister of Leonard Hofstadter and Michael Hofstatder. She has never appeared on the show, but has been mentioned a couple of times. She is mentioned to be a cutting-edge medical researcher working with gibbons to cure diabetes.

She is presumably 7 years older than Leonard and unknown how older she is than Michael. This was because Leonard mentions in The Cohabitation Formulation that she is 38 years old and married after Raj was mad at him for spending the night with his sister Priya.