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 spirituality and culture. Sergius played a significant role in the development of monastic life in Russia and is revered for his commitment to prayer, humility, and community. Sergius of Radonezh is also recognized for his influence during the Mongol invasion of Russia, promoting unity among the Russian principalities. He was canonized as a saint in 1422, and his feast day is celebrated on September 25 in the Orthodox Church.