Paid in Grain

There is a well-known story of the man who invented chess. The local ruler was so pleased with the invention that he offered the inventor a great reward of a million gold coins. The inventor suggested an alternative reward: he would get one gold coin on the first square of the chess board, two gold coins on the second square, four on the third, eight on the fourth, etc., doubling the number of gold coins each time. The ruler saw that this must be a much better deal for him, and accepted. The board has 64 squares. How many total gold coins did the ruler have to pay the inventor?