The name of Father Christopher Clavius, born in Bamberg, Bavaria (Germany) in 1537, is tied to a history of faith, mathematics and astronomy. Details regarding his early years are few. He entered the Jesuit order when he was 17. During his first visit to Rome, he was received by the actual founder of the Society of Jesus, Saint Ignatius of Loyola. He was sent for studies to the University of Coimbra and inthis city he observed for the first time a total eclipse of the sun, an event which created a passionate interest in astronomy. He returned to Rome to complete his studies in philosophy and theology. In 1567 he took the place of Spanish professor Baltasar Torres in the mathematics faculty of the Roman College, a position he held until 1595. During that time he produced a rich body of scientific texts on arithmetic, geometry, algebra and astrolabe. He was known as 'The Euclid of the Sixteenth Century'. He made important contributions to the commission set up by Pope Gregory XIII to reform the julian calendar. The new “Gregorian calendar”, named in honor of the Pope who promoted it, was adopted over time by all Catholic countries starting in 1582. He studied the new trends in astronomy and focused in particular on work by Copernicus, Kepler and Galileo. He produced a great amount of correspondence with the most important european scientists, a testimony to his spirit of scientific inquiry which permeated his entire life until his death in Rome on 12 February 1612. One of the largest lunar craters, Clavius, is named after him, as are other lunarcraters with the names of Jesuit scientists, a testimony to the contribution the Society of Jesus has made to science.