As I may have mentioned once or twice, many people assume that because Barack Obama is of mixed ancestry, he naturally identifies with all his ancestral races, as does, say, Tiger Woods or Ward Connerly. In reality, Obama has instead felt the constant need to prove he is black enough.
I'm looking for more examples of this phenomenon of feeling the need, due to your unusual background, to prove you are X enough. Perhaps actress Halle Berry? Maybe Zach de la Roccha of Rage Against the Machine is an example. (Daniel Day-Lewis is an amusing example of something slightly different: a complete insider -- his father was Poet Laureate of England and his maternal grandfather ran England's top movie studio -- who has used all his Method acting skills to convince himself that he is a much-discriminated against Irishman). Or Eamon de Valera of Ireland, although I'm not really familiar with his personality. In a different way, Hitler, Napoleon, and Stalin were all from the peripheries of empire.
I think there must be more. Do you know of any?