African king is history's richest man

Bill Gates who? CelebrityNetWorth has named Mansa Musa I, the 14th century leader of the Empire of Mali, the richest man of all time, with a personal worth of over US$400 billion.  Mali's role as supplier of salt and gold to much of the known world made the king rich and Mali an economic superpower.

Mansa Musa is not the lone medieval figure cavorting with the Carnegies and the Astors.  It  turns out that invading England can be a very profitable business. William the Conqueror and several of his closest allies are on the list. 

English noblemen John of Gaunt and Henry Duke of Lancaster are also in the top 25.