are immigrants allowed to compete in the olympics?

Question

which country do they represent..? the country they left or went to? seems a little unorthodox to have an african compete as an American, regardless of their citizenship status. 

Answer 1

The Olympics require competitors to be "legal nationals" of the countries they represent at the Games. 

I knew a guy whose dream was to compete in the Olympic games.  He was a talented college athlete but was unable to crack the top amateur rankings.  He emigrated to a smaller country and actually gave up his American citizenship specifically to qualify for their Olympic team, which he did.