If you go to Forbes page and take a look at the top richest people in the world, you will shocked by the size of their wealth. But none of their wealth could possibly come close to John Rockefeller's one.
His wealth was so significant that the was wealthier than Jeff Bezos, Bill Gates, Warren Buffet, Mark Zuckerberg and Elon Musk combined.

John Rockefeller was the richest American to ever live with an estimated wealth of $400 Billion.

How Exactly He Made That Fortune?

First, let's take a look at how he got into business in the first place.

He grew up in a large and controversial family, with a con man father and religious mother. He was so desperate to take care of his mom that he got a job as a bookkeeper at the age of 16. This job played an essential role in his life. In fact, it was so vital that he later ascribed all of his success to his first job, because there he learned how business works, from negotiating to collecting debts.

By the age of 19, he already mastered the game and decided to start his own business and began selling everything he possible could, from meat to grains and go a got a commission on every deal. Although that he was doing pretty good, his business only soared with the outbreak of the civil war, because the demand for food only increased.

His ambitions were more significant than that. With the discovery of oil in 1859, he realized potential opportunity.

John built his first refinery in 1863. Since the industry was still at its initial phase, most refiners could only turn 60% of the oil to Kerosene while dumping the rest into rivers. It was clearly a waste of resources for John, so he operated at a higher efficiency. And in less than 2 years, the business was worth over a million dollar.

By 1870, they were too big for a partnership, so he incorporated it into Standard Oil of Ohio. With its massive size and tremendous resources, the company started growing at an incredible speed. He would buy the least efficient competing refineries, throw money into it to improve their efficiency, use his power and network to get the highest possible discounts on oil shipments and get rid of his competitors.

Those who refused to sell, John would threatened them to start a price war until they would run out of cash and go bankrupt and then he would buy their assets cheaply at an auction.
That's how he took control of the entire industry.

Rockefeller realized that pipelines can easily replace the railroads to transport oil, so he began to built and acquire them. The railroads saw that as a threat that standard oil will take over the transportation industry as well.
At this point, Rockefeller was so big that there were many journalists, politicians and other businessmen who attached him to bring him down. Even the Congress saw him as a threat.

Although that he broke down the company into 41 entities under the banner of Standard Oil Trust, it didn't save him, and by 1911, the US Supreme Justice Department found Standard Oil guilty in violation of Antitrust Act, and broke it down in 34 different companies while John still kept his share.

It might seem like it was a disaster for him, but it turned out to be immensely profitable. Each of these companies individually were worth more with further increased Rockefeller's net worth to $400 billion.

Over time these companies either worked together or simply merged such as Chevron or Exxon Mobil, who are still leading the industry today.