I remember reading about Red Cloud in elementary school. It was part of a series entitled The Library of American Heroes. Here's what the book looked like. It was published in 1965. I hadn't realized there was an autobiography, which I'm sure would be much more telling.
One of my favorite books I read later in high school was Black Elk Speaks, although I've since read reviews that John Neihardt took a lot of liberties in this "oral history." But, still it was a mesmerizing book especially as Black Elk related his time in London and his out of body experiences, in which he returned to his native land.
Richter noted that it was very difficult to translate native languages into English or any other European language, as the structures were very different, not to mention the lack of comparable words to express what the natives actually felt, especially in regard to John Elliot's Tears of Repentance, noted in the previous post. At least in later years there was an attempt to try to capture these great chiefs' thoughts with a wider audience in mind. I also think such books helped immortalize many of these former Indian leaders, for better and for worse, making them an indelible part of the American experience.