This is a biography of the Sergii named Radonezhskii (1314-1392), the founder and Father Superior of the Troitse-Sergii monastery. He became known by his contemporaries also as: a supporter of cenobitical living of monks, a new form of monastic life at that time in Rus; a peacemaker who helped Russian princes listen to each other and stop their conflicts; a person who lived his life by evangelic teaching and followed his Christian and monastic duties. This biography based mostly on the Life of Saint Sergii Abbot and Miracle worker of Radonezh by the well known Russian religious writer of late 14th-early 15th, monk Epiphanii the Sage, who spent many years in Troitse-Sergii monastery and two other works by the historian of Russian Orthodox church E. Golubinskii and the historian V. Kliuchevskii. Bibliography (163 items), chronology and comments.