A great source of quiz questions is the "What nationality is/was . . . ?", and we do have quite a lot in our database.
Most of the time it is quite obvious what nationality a person is. Take Ronald Reagan for example - every US President must be born in the USA, and he lived there all his life. So clearly Ronald Reagan was American.
Similarly with Pele, the footballer, who was born in Brazil and played for Brazil. There is no question that Pele was Brazilian.
But it can get more complicated.
Albert Einstein was born in Germany, renounced his German citizenship, gained Swiss citizenship, regained German citizenship, and finally became a US citizen! In this type of situation we tend to restrict our questions to "What nationality was . . . born?".
And the we have the United Kingdom, a complicated place that is covered in our Blog Post The British Isles - An Explanation. In short, there are three countries in Great Britain (GB), a fourth is added for the United Kingdom (UK), and all four countries, GB and the UK all compete in various sports at different times.
For anyone who has competed for one of the four individual countries in any sport, we use that country as their nationality - Gareth Bale played football for Wales, so we have the answer Welsh. As a quizmaster using one of our quizzes you could accept British if you want.
In other cases we use our discretion. The former Leader of the Scottish National Party, Nicola Sturgeon is very clearly Scottish.
However, J K Rowling seems to identify as British, having been born in England and lived in Scotland.
This is not an easy area, but we hope we have been consistent in our approach.