This list is biased toward Americans and Englishmen. I'm sure there are many others who deserve to be in the top 25. There are other problems; for example, property values in the middle ages are probably inflated. Nevertheless, it's an interesting list of men (no women). They are ranked by their estimated net worth in 2012 inflation-adjusted American dollars. You can find out more details at: The 25 Richest People Who Ever Lived – Inflation Adjusted.
There don't appear to be any scientists (or philosophers) on the list. Three of my ancestors are on the list (#6, #15, and #16) but I didn't inherit a penny.
- Mansa Musa I of Mali (1280-1337): $400 billion
- The Rothschild family: $350 billion
- John D. Rockefeller (1839-1937): $340 billion
- Andrew Carnegie (1835-1919): $310 billion
- Tsar Nicholas II of Russia (1868-1918): $300 billion
- Mir Osman Ali Khan (1886-1967): $230 billion
- William The Conqueror (1028-1087): $229.5 billion
- Muammar Gaddafi (1942-2011): $200 billion
- Henry Ford (1863-1947): $199 billion
- Cornelius Vanderbilt (1794-1877): $185 billion
- Alan Rufus (1040-1093): $178.65 billion
- Bill Gates (1955 - ): $136 billion
- William de Warenne ( -1088) $147.13 billion
- John Jacob Astor (176-1848): $121 billion
- Richard FitzAlan (1306-1376): $118.6 billion
- John of Gaunt (1340-1399): $110 billion
- Stephen Girard (1750-1831): $105 billion
- Alexander Turney ("A.T.") Stewart (1803-1876): $90 billion
- Henry of Grosmont (Duke of Lancaster) (1310-1361): $85.5 billion
- Friedrich Weyerhauser (1834-1914): $80 billion
- Jay Gould (1836-1892): $71 billion
- Carlos Slim Helu (1940- ): $68 billion
- Stephen Van Rensselaer (1764-1839): $68 billion
- Marshall Field (1834-1906): $66 billion
- Samuel ("Sam") Moore Walton (1918-1992): $65 billion
- Warren Buffett (1930 - ): $64 billion