4. Cornelius Vanderbilt, $185 Billion
After quitting school at 11, Cornelius Vanderbilt started a small ferry business, which resulted in him buying a steamboat and getting in with a very powerful businessman named Thomas Gibbons, who taught him how to be a smart businessman. When Gibbons died, Vanderbilt stayed on with Gibbons's son, and then bought him out.
Little by little, Vanderbilt gained control of the ferry lines around the city and made a secret monopoly by having an under-the-table partnership with a rival company. Since his ferry business grew around the time of the railroads, he became involved with the latter, since railroad routes often relied on steamships.
Meanwhile he bought a ton of land in New York and after the Gold Rush, Vanderbilt got into ocean liners, later taking the railroad business to the next level. He invested in a handful of railroad companies, including the New York and Harlem Railroad, and built Grand Central Terminal. Just outrageous wealth.