Sergius of Radonezh (Venerable Sergii Radonezhsky, Сергий Раднежский, 1314-1392) - was the greatest spiritual leader and monastic reformer of the medieval Russia. Together with Seraphim Sarovsky, he is the most venerable of the Russian saints.
As his medieval Life states, he was born to a boyar family near Rostov the Great, where the Varnitsy Monastery now stands (http://www.varnitsky-monastir.ru/). His parents Kirill and Maria became impoverished and moved to Radonezh together with their 3 sons: Stefan, Varfolomei, and Peter. Upon his parents' death, Varfolomei went to Khotkovo near Moscow, where his elder brother Stefan ministered. He persuaded Stefan to find a more secluded place. In the deep forest on Makovets hill they decided to build a small cell and a church dedicated in honor of the Trinity. Thus started the history of the great Troitse-Sergiyeva Lavra.
After a while, Stefan moved to a monastery in Moscow. Varfolomei took monastic vows, taking the name Sergius, and spent more than a year in the woods alone as a hermit. Soon, however, others monks started coming to him and building their own cells. After some time, they persuaded him to become their hegumen, or father superior. Following his example, all the monks had to live from their own labour. Over time, more and more monks and donations came to this place. Nearby, there appeared a posad (settlement), which grew into the town of Sergiev Posad, and villages.
“Holy Vision to Youth Varfolomey”, by Mikhail Nesterov (1890). When the news of Sergii's life reached patriarch Philotheus of Constantinople, he sent to him a monastery charter, or kinoviya. During the reign of Dmitriy Donskoy, his disciples started to spread his teaching across the central and northern Russia. They settled in most impracticable places and founded numerous monasteries, of which the Borisoglebsky, Ferapontov, and Kirillo-Belozersky Monasteries should be mentioned. St. Sergius was also connected with the foundation of two monasteries in Moscow – the Andronnikov and the Simonov Monasteries. All in all, disciples of Sergius founded about 400 monasteries, thus greatly extending the geographical extent of his influence and authority. However, when the Metropolitan Alexius asked him to become his successor, Sergii declined, preferring to remain a simple monk.
As an ascetic, Sergii did not take part in political life of the country. However, he blessed Dmitry Donskoy when he went to fight the Tatars in the signal Battle on Kulikovo field. Some historians interpreted his political stance as aspiring to make peace and unite Russian lands under the leadership of Moscow.
Sergii died on September 25, 1392 and was canonized in 1452. His relics were found in 1422 and placed in the Troitse-Sergiyeva Lavra he founded. The church commemorates him on September 25, the day of his death, and on July 5, the day his relics were found. See September 25 (the Eastern Orthodox liturgics). The Fellowship of Saint Alban and Saint Sergius is named in part for him.