George Armstrong Custer...Quizmonster is partially correct, he had been a Brevet General in the US Civil War, but reduced in rank when the war was over...
A 'brevet' officer in the USA in Custer's day was what would be called in the British Army one who was "acting/unpaid". In other words, not really a General at all. In terms of the actual question, no general was defeated at The Little Big Horn.