French Protestant pastor Paul Sabatier was the first modern biographer of St. Francis of Assisi. His book, first published in French in 1894, quickly became a best seller throughout Europe and was translated into English and published in the U.S. by 1906. Francis has been the most popular saint in the world ever since.
There have been many great books on St. Francis in the century since Sabatier, a few of them immortal. My favorite has always been G. K. Chesterton’s St. Francis of Assisi (1923); Chesterton really knew how to cut to the heart of a subject. And Nikos Kazantzakis’s penetrating novel Saint Francis (1956) still has the power to move readers, even after Martin Scorcese made his crazy film adaptation of it in the early 1980s.