John Bogle, founder of the Vanguard Group and pioneer of index funds, may have saved investors more money than anyone else in history. By some estimates, his crusade to drive down fees has, over the past five decades, left them with more than $1trn that would otherwise have gone to fund managers. Index funds, through which speculators can invest in the stockmarket as a whole, cut out the middlemen. In doing so, they have transformed the world of investing.