The man in the photo resembles the photo of John Roll that appeared in Ida Tarbell's McClure's articles about Lincoln's early life (without the large chin beard):
Hint #4: According to this man, the last conversation he had with Abraham Lincoln was during the time period when Lincoln was President-elect. What Lincoln told him is included in some Lincoln biographies (including David Herbert Donald's).
It's really not that hard, Joe. The folks who have followed one particular topic (which has been thoroughly discussed on this forum), will recognize the name once someone correctly answers the question.
It is mentioned in Donald's book. However, it is not mentioned in the section that deals with the period when Lincoln was President-elect. It is mentioned when Donald discusses the one particular topic I mentioned previously. This particular topic deals with something that happened much earlier in Lincoln's life than when he was President-elect. The man who is the answer to the trivia question had something to say about this topic.