As part of his research, Hill interviewed many of the most famous people of the time, including Thomas Edison, Alexander Graham Bell, George Eastman, Henry Ford, Elmer Gates, John D. Rockefeller, Sr., Charles M. Schwab, F.W. Woolworth, William Wrigley Jr., John Wanamaker, William Jennings Bryan, Joseph Stalin, Theodore Roosevelt, William H. Taft, Woodrow Wilson, Charles Allen Ward and Jennings Randolph. The project lasted over twenty years, during which Hill became an advisor to Carnegie
http://en.wikipedia.org/wiki/Napoleon_Hill