Thirty-first president of the United States, serving from 1929 to 1933.
In 1966, when a note marked 'H.H.' is found on the body of the latest in a string of murder victims, despite having Hawaiian detective Harry Hoo on the scene with him, Maxwell Smart initially considers the now deceased former president the more likely suspect. [Episode #38: "Hoo Done It".]
The following year, after a meeting at the White House, 91-year-old reactivated former CONTROL Chief Admiral Harold Hargrade refers to the president as "Herbert", When informed that Herbert Hoover is no longer president the Admiral remarks that it's too bad because he thought Hoover had shown "a lot of promise". [Episode #59: "A Man Called Smart, Part 3".]