Jagiello of Lithuania was the Grand Duke of Lithuania and King of Poland in the 14th and 15th centuries. He was a significant figure in the history of Eastern Europe, known for his role in the union between the Kingdom of Poland and the Grand Duchy of Lithuania, which laid the foundation for the Polish-Lithuanian Commonwealth. Jagiello's reign was marked by territorial expansion, diplomatic alliances, and efforts to strengthen the unity of the Polish and Lithuanian states. He is also remembered for his conversion to Christianity and the subsequent spread of Christianity in the region. Overall, Jagiello of Lithuania played a crucial role in shaping the political and cultural landscape of Eastern Europe during his time.