The Law of Success
As part of his research, Napoleon 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, Charles M. Schwab, F.W. Woolworth, William Wrigley Jr., John Wanamaker, William Jennings Bryan, Theodore Roosevelt, William H. Taft, Woodrow Wilson, and Jennings Randolph.
The project lasted over twenty years, during which Hill became an advisor to Carnegie. The formula for rags-to-riches success that Hill and Carnegie formulated was published initially in 1928 in his book The Law of Success.