Walter Wetzel was President of National Congress of American Indians from 1960-1964 as well as being Chairman for the Blackfoot Indians. He went to the Redskins office with pictures of Indians asking that the Redskins use these images to help design a new helmet logo.
Here is an article from the Washington Post back in 2002 by Marc Fisher, where he interviewed Walter Wetzel as part of his article. Wapo has made it so the article is no longer viewable (I guess Mike Wise has more clout there than we thought), so you have to view it through second hand sources, such as this one. But I found multiple sources with this very same article. The relevant info is in the last couple of paragraphs.
Indianz.Com - American Indians Among Admirers Of Redskins Name