Conversation so far:
What about William Henry Dietz heritage was contested?
Dietz's heritage was first contested in 1916 after former neighbors who settled on the Pacific Coast heard he was posing as an Indian.
Was William Henry Dietz living on an Indian reservation or had he lived on one before?
It is not confirmed whether William Henry Dietz actually was born on the Pine Ridge reservation in South Dakota or not.

Question: Who was Dietz impersonating when the FBI investigated him?
Self-contained rewrite: Who was William Henry Dietz impersonating when the FBI investigated him?