The list of the wealthiest historical figures is an attempt to gather and compare the net-worth and fortunes of historical figures against one another; it does not include living billionaires. The single most important measure in this list is gauging the wealth as a percentage of the GDP of the USA in that respective period. The figures shown are at the same percentage of the current GDP. Inflation and other factors devalue currency over time; economies of different regions over time periods; and economies' produced goods, commodities, and services over time. These fluctuations increase difficulty when accurately assessing and comparing fortunes from different decades, centuries, and especially millennia for the economy of any given State or region. Also, because several individuals and families never had their financial records revealed publicly and there are no contemporary estimates of their net-worth, several people could be omitted due to a lack of citable estimates of their net-worth. Some estimates of personal wealth are based upon ownership of capital and stock in a company or many companies, the value of which is always changing.