The photograph showed the son, but my eye gravitated toward the mother. That first glimpse was surprising — the stout, pale-skinned woman in sturdy sandals, standing squarely a half-step ahead of the lithe, darker-skinned figure to her left. His elas­tic-band body bespoke discipline, even asceticism. Her form was well padded, territory ceded long ago to the pleasures of appetite and the forces of anatomical destiny. He had the studied casualness of a catalog model, in khakis, at home in the viewfinder. She met the camera head-on, dressed in hand-loomed textile dyed indigo, a silver earring half-hidden in the cascading curtain of her dark hair. She carried her chin a few degrees higher than most. His right hand rested on her shoulder, lightly. The photograph, taken on a Manhattan rooftop in August 1987 and e-mailed to me 20 years later, was a revelation and a puzzle. The man was Barack Obama at 26, the community organizer from Chicago on a visit to New York. The woman was Stanley Ann Dunham, his mother. It was impossible not to be struck by the similarities, and the dissimilarities, between them. It was impossible not to question the stereotype to which she had been expediently reduced: the white woman from Kansas.

The president’s mother has served as any of a number of useful oversimplifications. In the capsule version of Obama’s life story, she is the white mother from Kansas coupled alliteratively to the black father from Kenya. She is corn-fed, white-bread, whatever Kenya is not. In “Dreams From My Father,” the memoir that helped power Obama’s political ascent, she is the shy, small-town girl who falls head over heels for the brilliant, charismatic African who steals the show. In the next chapter, she is the naïve idealist, the innocent abroad. In Obama’s presidential campaign, she was the struggling single mother, the food-stamp recipient, the victim of a health care system gone awry, pleading with her insurance company for cover­age as her life slipped away. And in the fevered imaginings of supermarket tabloids and the Internet, she is the atheist, the Marx­ist, the flower child, the mother who abandoned her son or duped the newspapers of Hawaii into printing a birth announcement for her Kenyan-born baby, on the off chance that he might want to be president someday.

The earthy figure in the photograph did not fit any of those, as I learned over the course of two and a half years of research, travel and nearly 200 interviews. To describe Dunham as a white woman from Kansas turns out to be about as illuminating as describing her son as a politician who likes golf. Intentionally or not, the label obscures an extraordinary story — of a girl with a boy’s name who grew up in the years before the women’s movement, the pill and the antiwar movement; who married an African at a time when nearly two dozen states still had laws against interracial marriage; who, at 24, moved to Jakarta with her son in the waning days of an anticommunist bloodbath in which hundreds of thousands of Indonesians were slaughtered; who lived more than half her adult life in a place barely known to most Americans, in the country with the largest Muslim population in the world; who spent years working in villages where a lone Western woman was a rarity; who immersed herself in the study of blacksmithing, a craft long practiced exclusively by men; who, as a working and mostly single mother, brought up two biracial children; who believed her son in particular had the potential to be great; who raised him to be, as he has put it jokingly, a combination of Albert Einstein, Mahatma Gandhi and Harry Belafonte; and then died at 52, never knowing who or what he would become.

Obama placed the ghost of his absent father at the center of his lyrical account of his life. At times, he has seemed to say more about the grandparents who helped raise him than about his mother. Yet she shaped him, to a degree Obama has seemed increasingly to acknowledge. In the preface to the 2004 edition of “Dreams From My Father,” issued nine years after the first edition and nine years after Dunham’s death, Obama folded in a revealing admission: had he known his mother would not survive her illness, he might have written a different book — “less a meditation on the absent parent, more a celebration of the one who was the single constant in my life.”