Among his volumes of fan mail, Twain often found photographs of men claiming to be his double. By way of reply, he would send the following form letter:
"My dear Sir, I thank you very much for your letter and your photograph, In my opinion you are more like me than any other of my numerous doubles. I may even say that you resemble me more closely than I do myself. In fact, I intend to use your picture to shave by. Yours thankfully, S. Clemens."
[Which movie stars have received the most fan mail in one year? Mickey Mouse (800,000 in 1933) and Shirley Temple (730,000 in 1936).]
Sources
E. Fuller, 2500 Anecdotes
