Hermannus of Cologne was a notable 12th-century scholar and theologian from Cologne, Germany. He is best known for his work in the field of astronomy and for his contributions to the study of the calendar. Hermannus played a significant role in the introduction of the Gregorian calendar in Europe, which aimed to correct inaccuracies in the previous Julian calendar. In addition to his astronomical work, Hermannus was also involved in the education of clergy and the promotion of scholasticism. His writings reflect a blend of classical knowledge and Christian thought, making him an important figure in the intellectual landscape of the Middle Ages.