John D. Rockefeller was the wealthiest American to ever live, and possibly the wealthiest man in history.
At the time of his death, his estimated net worth was $340 billion dollars (adjusted for today’s worth). That is four times more than Bill Gates’ current fortune.
He was born July 8, 1839, in Richford, New York in a family of modest means. His father, William Avery “Bill” Rockefeller, owned a small farm and was a salesman of somewhat ill-repute who fathered eight children between his wife and mistress. Bill would leave the family intermittenly and taught his sons that they must get the best of any deal they made with anyone. John’s mother, Eliza Davison, did the best she could to keep a stable and strict home for her children. She taught John to not be wasteful and to be giving. 
The family moved to Cleveland, Ohio in 1853 where John did well in mathematics and graduated from Cleveland Central High School. He was hard-working and industrious and landed his first job when he was 16 years old as a bookkeeper. A few years later, John partnered with another man in a commission merchant venture, dealing in various goods such as meat and feedstock. They were highly successful and John had made a small fortune in just the first year. 
In 1859, oil was discovered in Titusville, Pennsylvania and by the 1860s the oil boom began. John quickly decided that this was where his capital and efforts ought to be, so he opened an oil refinery near Cleveland in 1863. In a matter of a few years, it was the biggest in the area. 
The Standard Oil Company was founded by John in 1870.
John was aggressive and quick with his business moves and acquisitions. He bought out nearly everyone in the Cleveland area and sought to control every aspect of the oil business in-house. By the early 1880s, Standard Oil was a true monopoly. It controlled 90% of the oil in the United States and each sector of the oil business was consolidated under its’ name. 
The U.S. government and the public took notice of Standard Oil’s monolithic takeover and passed the Sherman Antitrust Act of 1890. The State of Ohio followed suit and decided Standard Oil violated the law. John saw the writing on the wall and broke apart the company into smaller pieces and relegated their leadership to others. However, this did not effectively change anything except keep the government at bay. 
Nine years later, John decided to bring the company together again in a holding company but a 1911 decision by the U.S. Supreme Court citing the Sherman Antitrust Act, forced the company to again break apart. This only made John D. Rockefeller wealthier as the 34 entities that resulted from the dissolution would become more valuable separately than as a whole.  A remarkable commercial legacy would follow. Some of the companies that came from Standard Oil: Esso, ExxonMobil, Imperial Oil, Socony,
Chevron, Amoco, ARCO, and Marathon. 
In his later years, John D. Rockefeller established a philanthropic legacy that is felt today.
During his life he gave $500 million dollars to various causes both educational and scientific. The University of Chicago and Spelman College sprung directly from his pockets. Most famously perhaps was the formation of the Rockefeller Foundation which strives to “promote the well-being of humanity throughout the world”.