Hartford "Sonny" Black Eagle Jr. died last Monday at his home in Lodge Grass on the tribe's reservation in the southeastern part of the state, said his son, Crow tribal Chairman Cedric Black Eagle.
The 78-year-old traditional healer died in his sleep after battling respiratory problems stemming from a severe case of pneumonia several months ago, Cedric Black Eagle said.
Obama called Black Eagle's wife, Mary, on Wednesday to express his condolences, a White House official said.
Hartford Black Eagle and his family adopted Obama when the candidate visited the reservation in the weeks leading up to Montana's Democratic primary.
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As part of the adoption, Obama attended a purification ceremony where he was prayed over by Black Eagle and received a Crow name that translates as "One Who Helps People Throughout the Land." Cedric Black Eagle said his father considered the 2008 adoption ceremony one of the proudest moments in his life and subsequently considered it his duty to make sure Native American voices were heard.
"He felt like he was representing all of Indian Country as a spokesman, and always telling his [adopted] son, the president, that he has to make sure all of the people in Indian Country are heard and try to help them all," Cedric Black Eagle said.
Hartford Black Eagle and his wife attended Obama's presidential inauguration and several Christmas dinners at the White House, said his son.
During destructive flooding on the reservation last year that left Lodge Grass largely isolated and forced many tribal members from their homes, Obama called Hartford and Mary Black Eagle to check on their safety, Cedric Black Eagle said.
Hartford Black Eagle was born during the Great Depression and grew up on his family's ranch outside Lodge Grass.
After his mother died of tuberculosis when he was a baby, Black Eagle was raised by his grandparents and later became a strong advocate for preserving the Crow's traditions and culture.
He taught the Crow language to his eight children, and instructed them and others in the community on performing traditional tribal dances, Cedric Black Eagle said.
To earn a living, he worked as a carpenter, an Indian Health Service representative and, most recently, as a political adviser to his son, who recently lost a bid for re-election.
His death came less than two weeks after the loss of another member of the family, 55-year-old daughter Marilyn Black Eagle, who died Nov. 16 in a two-vehicle accident.
Funeral services for Hartford Black Eagle were Thursday. He was buried at Lodge Grass Cemetery.