From the mentalfloss.com article:
You always hear about how rich Bill Gates is, how rich Oprah is, how rich J.K. Rowling is. But none of them even make the top 10 richest people of all time. Compiled by Forbes magazine, this a list of the wealthiest people ever (EVAR!). They ranked these bazillionaires (my term, not theirs) according to the total GDP of the nation they lived in and adjusted their net worths to account for inflation as of 2007.
Read the article here.