John D. Rockefeller is the richest American who ever lived. At the time of his death in 1937, Rockefeller was worth the equivalent of $340 billion in today's dollars. His company Standard Oil dominated American Oil production and was eventually broken up by The US Government for being a monopoly. Standard Oil was broken into smaller companies that you probably recognize today: Amoco, Chevron Conoco, and ExxonMobil. Rockefeller was the first American to ever have a net worth over $1 billion.