What is a common description of john d rockefeller and andrew carnegie​

But when he was 38 he started the Keystone Iron Works, and he stayed with that until 1901. By then Keystone Iron had become U.S. Steel, and Andrew Carnegie had become one of the wealthiest men on the planet. John D. Rockefeller went into business when he was 20, and he picked up his first oil well as a sideline.

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