Saint Sergius of Radonezh was a prominent Russian Orthodox monk and spiritual leader, born in 1314. He is best known for founding the Trinity Lavra of St. Sergius, a major monastery near Moscow that became a center of Russian monasticism. Sergius played a crucial role in the spiritual revival of Russia during the 14th century, promoting a life of prayer and asceticism. He is venerated as a saint in the Eastern Orthodox Church and is celebrated for his deep faith and commitment to God. Saint Sergius is also recognized for his efforts in uniting the Russian principalities during a time of external threats, particularly from the Mongol Empire.