Callixtus II was a pope who served from 1119 to 1124. He was born as Guido di Castello and became known for his efforts to strengthen the authority of the papacy. His papacy was marked by the resolution of the Investiture Controversy, a conflict between the church and secular rulers over the appointment of bishops. During his time, Callixtus II also worked to promote peace in Europe, particularly through the Treaty of Vienne in 1122, which helped to settle disputes between the church and the Holy Roman Empire. His leadership contributed to the stability of the church during a tumultuous period in history.