Better explanation: "John D. Rockefeller, who became the world’s first billionaire in 1916, a sum equal to $30 billion today, adjusted for inflation. In a sense, this underestimates the oil scion’s wealth. By the time Rockefeller died in 1937, his assets equaled 1.5% of America’s total economic output. To control an equivalent share today would require a net worth of about $340 billion dollars, more than four times that of Bill Gates, currently the world’s richest man."
http://www.forbes.com/sites/carlodonnell/2014/07/11/the-rock...