Barack Obama's story, spanning from his mother's roots in Kansas to his father's in Kenya and his childhood spent in Hawaii and Indonesia, has been well chronicled and a central part of his allure as a candidate who transcends national and racial lines. But one small part might have remained largely hidden from public view. In a first-floor apartment of a brick public housing complex on a side street in South Boston lives a woman who city officials believe is Obama's aunt. Her name is Zeituni Onyango, as in the "Auntie Zeituni" in one of his books, a polite and...