The dates of his birth and of his becoming a Franciscan are not known; but he was one of the small group of most trusted companions of, the saint during his last years. He was a native of Assisi and was one of Francis's first companions, and became his secretary and confessor.
After Francis's death Leo took a leading part in the opposition to Elias of Cortona: he it was who broke in pieces the marble box which Elias had set up for offertories for the completion of the basilica at Assisi. For this Elias had him scourged, and this outrage on St Francis's dearest disciple consolidated the opposition to Elias and brought about his deposition.
Leo was the leader in the early stages of the struggle in the order for the maintenance of St Francis's ideas on strict poverty, and the chief inspirer of the tradition of the Spirituals on St Francis's life and teaching. The claim that he wrote the so-called Speculum perfectionis cannot be allowed, but portions of it no doubt go back to him.
A little volume of his writings has been published by Lemmeus (Scripta Iratris Leonis, 1901). Leo assisted at Saint Clara's deathbed, 1253; after suffering many persecutions from the dominant party in the order he died at the Porziuncola in extreme old age.
All that is known concerning him is collected by Paul Sabatier in the "Introduction" to the Speculum perfectionis (1898).
Brother Leo in Literature
Brother Leo figures prominently in Nikos Kazantzakis' book Saint Francis, or God's Little Pauper. In this book, Leo is portrayed as Francis' constant companion. Leo is utterly faithful and steadfast, and yet struggles with his own shortcomings while following Francis.