The Illinois senator who is leading rival Hillary Clinton in their race for the party's presidential nomination, joined the Crow Nation, a tribe of some 12,100 members in Montana, taking on a native name and honorary parents in a traditional ceremony.
Obama, who would be the first black US president, was "adopted" by Hartford and Mary Black Eagle and given a name which means "one who helps all people of this land."
"I was just adopted into the tribe, so I'm still working on my pronunciation," Senator Obama told a crowd after stumbling over some of the native names.
"His heritage of being poor, of being an outsider, you know those two things are the commonalities that he has with us," he said.
"We've always been treated like outsiders when it comes to government policy. In addition to that, we all grew up poor."