20. William Weightman

richest americans
  • Adjusted wealth*: $51.8 billion
  • Lived: 1813-1904

Weightman founded a drug company that developed a synthetic form of quinine, which is used to treat malaria. The firm was later absorbed into Merck (MRK).

He also made money off substantial investments in Philadelphia real estate.

First published June 2, 2014: 6:18 PM ET
Source: *Most nominal wealth estimates are from The Wealthy 100 by Michael Klepper and Robert Gunther, and include wealth at time of death, including bequests. Estimates were then calculated as a fraction of the overall economy at time of death by Sam Williamson of Measuring Worth, and then presented in 2013 dollars based on the size of the current U.S. economy. Estimates for Gates and Buffett provided by Wealth-X.

Biographical information from The Wealthy 100 by Michael Klepper and Robert Gunther, Encyclopedia Britannica, and The Prize by Daniel Yergin.