Who is this person?

[Eva Elisabeth]

Very smart guess, Linda, but, sorry, it's not Townsend either.

Hint #5: He was from Indiana, and his father a German immigrant.

Hint #6: The friendship I mentioned in hint #4 began with a letter this gentleman (when he was a college boy) wrote the other person in request for a Lincoln autograph. Later it resulted in a common Lincoln-related project.