500
The Knights Templar was an organization that existed for nearly two centuries during the Middle Ages. Starting with founder Hugues de Payens in 1118–1119, the Order's highest office was that of Grand Master. How many Grand Masters did not die while in office?
All but two of the Grand Masters died in office, and several died during military campaigns. Grand Master was a position which was held for life, though considering the martial nature of the Order, this could mean a very short tenure.