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 new parents in a traditional ceremony.
Senator Obama was adopted by Hartford and Mary Black Eagle and given a name which means "one who helps all people of this land".
"I like my new name, Barack Black Eagle," he said.
"That is a good name."
The state is home to some 60,000 American Indians, making them a key swing vote.
Senator Obama said he would appoint a Native American advisor to his senior White House staff.
Crow Nation welcomes Barack Black Eagle - World - BigPond News