Cyril of White Lake was a Russian monk born as Kozma in Moscow during the 14th century. After entering the Simonov Monastery around 1380, he became a disciple of Sergius of Radonezh. Seeking a life of quiet prayer away from public duties, he relocated to the shores of Lake Beloye with the monk Therapont. There, he established a strict monastic community that eventually grew into one of the largest religious centers in northern Russia.