20. Michael Bloomberg (b.1942)
> 2018 estimated net worth: $59.4 billion
> Source of wealth: Bloomberg L.P.
> Birthplace: Boston, Massachusetts
Michael Bloomberg worked on Wall Street at the beginning of his career but eventually created his own information technology company to serve the financial industry. His company quickly became successful thanks to the Bloomberg Terminal, which in 1981 began offering traders a computerized way to collect, analyze, and share data. Bloomberg eventually served as a three-term mayor of New York City.
19. Andrew Mellon (1855-1937)
> 2018 estimated net worth: $64.3 billion
> Source of wealth: Banking
> Birthplace: Pittsburgh, Pennsylvania
The son of wealthy banker Thomas Mellon, Andrew Mellon eventually took over his bank. The younger Mellon proved he had a keen eye for recognizing emerging technologies. He helped found the Aluminum Company of America and the Gulf Oil Corporation. He later served as a U.S. secretary of the Treasury for more than a decade.
18. Larry Ellison (b.1944)
> 2018 estimated net worth: $65.3 billion
> Source of wealth: Oracle
> Birthplace: New York City, New York
Larry Ellison founded Oracle software company in 1977. The company got its big break in 1981 when IBM opted to use Oracle’s database management system. Oracle is now one of the largest software company in the world.
17. Mark Zuckerberg (b.1984)
> 2018 estimated net worth: $66.0 billion
> Source of wealth: Facebook
> Birthplace: White Plains, New York
Mark Zuckerberg’s rise to prominence is well known. While at Harvard, he created the social media juggernaut Facebook. Despite the company’s recent problems with the security of its data, Zuckerberg is the nation’s wealthiest person under 40.
16. Henry Ford (1863-1947)
> 2018 estimated net worth: $68.3 billion
> Source of wealth: Automobiles
> Birthplace: Dearborn, Michigan
Henry Ford became one of America’s most famous entrepreneurs due to the dominance of the Ford Motor Company. Ford was able to make cars efficiently and inexpensively after inventing the moving assembly line. By 1918, nearly half of all cars on American roads were Fords.