Student or Learner
an American Express advert of famous Americans nobody recognised
The reference to the "advert" is to a series of TV commercials that featured people with famous NAMES or famous DEEDS -- but not famous faces.
The idea was that you need a well-recognized credit card (such as American Express) because when you travel, no one will recognize YOU.
This astronaut was famous for his DEED, but not particularly for his face. So the ad showed an ordinary person who turned out to be someone famous after all.