First Lady of the United States isn't an obscure "office," but the Second Lady -- as the wife of the vice president is occasionally called -- is considerably more so. Today is Muriel Humphrey's birthday, and so an appropriate moment to recall the spouses of the vice presidents (all wives so far, but someday the list will surely include husbands too).
Thus far there have been 38 second ladies, beginning with Abigail Adams in 1789. Six vice presidents had no wives during their terms because they were widowers; one -- William R. King -- because he'd never married. The last time there was no second lady was during Charles Curtis' vice presidency, since his wife Annie Curtis had died about five years before he took office.
As for Muriel Humphrey, she was born Muriel Fay Buck in South Dakota, attended Huron College, and married the future veep in 1936. After he died in early 1978, the governor of Minnesota appointed her to fill his Senate seat for most of the rest of that year. She declined to run in her own right -- after a life in politics with the Happy Warrior, she said she was tired of it. She remarried and lived in retirement until her death in 1998.