Which U.S. President did not appear as a mystery guest on the U.S. TV show "What's My Line?"

"What's My Line?" was a panel TV game show that originally ran in the United States on the CBS Television Network from 1950 to 1975 (original and syndicated formats). Before they became President of the United States, Jimmy Carter, Gerald Ford, and Ronald Reagan were public figures that appeared on the TV show "What's My Line?".

In 1974 (then-Governor of Georgia), Jimmy Carter was on the game show "What’s My Line?". Comments were made on how spiritual he looked. He was even asked if he had a job recruiting nuns. Also, Carter wasn't the first future president to appear on this show. Gerald Ford had made an appearance nearly five years before when was the U.S. House Minority Leader. The last one here to be on the show before he was U.S. President was Ronald Reagan. When he was Governor of California, he made an appearance on "What's My Line?".

President Richard Nixon is the person that never went on the game show either before or after he became President.