The term "self-made" is somewhat subjective in the world of wealth. Sure, there are billionaires who came from true poverty to strike it rich. But plenty of other so-called self-made rich people started out with affluent families and elite, expensive educations.
To try to fill in the gray areas, Forbes has come out with a "self-made score" for its billionaires. It's like a sliding scale of self-madehood. A score of 1 means they inherited everything. A score of 10 means they grew up poor and overcame "significant obstacles."
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So who are the most self-made billionaires? Among those who get a 10 are: Oprah Winfrey; Sheldon Adelson, the casino king who grew up sleeping on the floor of a Dorchester, Massachusetts, tenement house; and Harold Hamm, the fracking tycoon, who grew up in a family of Oklahoma sharecroppers. (The full spectrum of the list, and corresponding billionaires, is listed below.)