8. Herbert Hoover
Net worth:
$75 million
Famously an accomplished engineer, a Great Depression President, and the namesake and driving force behind the Hoover Dam. Unfortunately, history seems to agree he was better at running mines than the U.S.
How he made his riches
Herbert Hoover made his fortune in mining. First as a geologist and engineer, then by 23 years old he became a mine manager. He went on to work in China, eventually becoming the director of Chinese Engineering and Mining Corporation. Hoover eventually went into business for himself, and made the bulk of his fortune as a mining consultant for the British firm Burma Corporation. He was a wealthy man by the time he was 40.