Saint Jacek, also known as Saint Hyacinth, was a Polish Dominican friar born in the 13th century. He is recognized for his missionary work in Eastern Europe, particularly in Poland and Lithuania. Jacek is often depicted carrying a monstrance, symbolizing his dedication to the Eucharist and spreading the Christian faith. He founded several Dominican monasteries and played a significant role in the establishment of the order in Poland. Saint Jacek is celebrated for his piety and commitment to serving the poor, and he was canonized in 1594. His feast day is observed on August 17.