The famous French satirical writer, Voltaire, was worth $500,000 at the age of 40. But he did not earn his money from books.
Voltaire acquired most of his wealth by lending money to needy noblemen. He would lend an heir to an estate a large sum on condition that he would pay him annually 10 percent interest on the amount as long as both of them lived. The heir would be neither required nor allowed to pay off the principal, and the agreement ended only when Voltaire died. Voltaire picked only younger men and, because of his tubercular appearance, had no difficulty in getting clients. It is said that when a prospective buyer hesitated, Voltaire would cough in a way that always closed the deal.
Voltaire 1694 - 1778