John D Rockefeller
1839-1937
Estimated net worth in 2012: $300 billion

The oil baron was born at the right time, entering his 30s just as the oil revolution hit its stride. He would go on to create what became almost a monopoly provider of oil production and distribution in the United States, known as Standard Oil. His business began with his brother William, and the company quickly grew to become the largest oil refinery in the world within a few years.