The only billionaire in the country at the time, Rockefeller was the richest American of the 1920s by a considerable margin. Second and third on Forbes' 1918 Rich List were Henry Clay Frick and Andrew Carnegie, who had net worths of $225 million and $200 million respectively. That equates to $4.7 billion and $4.1 billion in today's money.

Both men had formed their own businesses, with Frick – who founded the H.C. Frick & Company coke firm in 1871 – later becoming the chairman of the Carnegie Steel Company.

At the time, Forbes reporters wrote: "Nine persons in every ten, if asked, 'Who do you think is the second richest man in America?' would instantly reply, 'Andrew Carnegie.' They would be wrong, according to our best-posted bankers. H.C. Frick, the coke king and steel magnate, is rated above Carnegie."

However, both men died in 1919, leaving the spot for the second-wealthiest American of the 1920s open...

The Richest Americans the Decade You Were Born