These characters are usually just mentioned or shown in a screen/background but with no lines.

“Mr. Wolowitz is the ex-husband of Mrs. Wolowitz, the father of Howard Wolowitz, and the...

Mr. Wolowitz

George Cooper Sr.

Mrs. Rostenkowski

“Dr. Hofstadter is the ex-husband of Beverly Hofstadter and the father of Leonard and Michael...

Dr. Hofstadter