St. Sergius of Radonezh (†1392) was a pivotal Russian Orthodox monk and mystic. After his family’s impoverishment, he moved to Radonezh and embraced monastic life, taking the name Sergius. In 1337, he founded the Holy Trinity Lavra, a spiritual center that revitalized Russian monasticism. Known for his humility, asceticism, and miracles, Sergius inspired countless disciples, establishing numerous monasteries. He blessed Prince Dmitry Donskoy before the 1380 Battle of Kulikovo, aiding Russia’s liberation from Mongol rule. Canonized in 1452, Sergius remains Russia’s patron saint, revered for uniting faith and nation.