He is first mentioned in "The Maternal Congruence" where Sheldon mentions that Leonard's family have chosen high-achieving partners and then saying Leonard was worried that his mother wouldn't approve of Leonard dating Penny due to her education status and her biggest achievement being memorising the Cheesecake Factory menus.
He is indirectly mentioned again in "The Cohabitation Formulation" when Leonard tells Raj that his sister is 38 and married when Raj said he would have his way with Leonard's sister because he wanted to get back at Leonard for going out with his sister Priya.
- Wife: Unnamed
- Father-in-law: Alfred Hofstadter
- Mother-in-law: Beverly Hofstadter
- Brother-in-laws: Leonard Hofstadter, Michael Hofstadter
- Sister-in-laws: Penny Hofstadter, Unnamed (via Michael)
- Unnamed nephews/nieces
- Uncle-in-law: Floyd
- Aunt-in-laws: Edna, Nancy, Unnamed
- Cousin-in-laws: Unnamed
- Grandfather-in-law: Unnamed
- Grandmother-in-law: Unnamed
- It is possible that this person could also be a woman, as Leonard never mentions a husband, since all he says is "My sister's 38 and married".
- This individual also has an unknown high-achieving job since Sheldon stated in "The Maternal Congruence" that Leonard's family have all chosen high-achieving partners.