1. John D. Rockefeller, $340 Billion
John D. Rockefeller was born to a con artist, but didn't take after his pop, and became a bookkeeper. After he gained some experience, he found some investors and put together a produce company. With that money, he invested in oil and built a refinery with a few others, who he soon bought out, putting him in a good position to take advantage of the post-Civil War economic boom. When the war ended, he had one of the main refineries, and founded Standard Oil.
With this new company, Rockefeller started buying competing companies and incorporating some questionable business practices. Standard was soon behind 90 percent of the country's oil, and in all petroleum products, not just oil oil. Not only was Standard everywhere, Rockefeller and Standard owned every part of the process, so they didn't have to rely on wholesale. Standard was ubiquitous as dozens of companies were under the banner "Standard Oil Trust." It was the first major "holding company" and became an invincible juggernaut in the American economy.
Rockefeller eased back on oil due to public criticism, and went after steel, clashing with Carnegie. Eventually, Standard was called out for its monopoly and told to break up. This, of course, proved extremely profitable for Rockefeller, who hit his high water mark of $900 million, or 1/44th of the United States gross national product.
Ethan Wolff-Mann is an editor at Supercompressor. He barely missed being on this list. Follow him on Instagram.