There are a few famous individuals who have knuckled down in the past to achieve a postgraduate degree of PhD without being awarded it in an honorary fashion. Given the high number of “celebrities” in the world today though, the number is relatively small, even when you consider those no longer with us.
Condoleezza Rice has her PhD in political science from the Graduate School of International Studies at University of Denver, USA.
Gordon Brown has his PhD in history from the University of Edinburgh, UK.
Martin Luther King Junior received a PhD in systematic theology from Boston University, USA.
Brian May, guitarist from Queen received his PhD from Imperial College, UK, after completing his thesis on zodiacal dust clouds.
This is of course not a definitive list, a lot of time has been spent (wasted?) searching for famous names though, ultimately ending up quite fruitless! Of course one’s perception of a celebrity could be quite different to another’s. If you start to consider those recognised with a Nobel Prize or past inventors, then the list certainly starts to grow.
Any additions would be welcomed as a comment below.