Pope Gregory XIII (Latin: Gregorius XIII), born Ugo Boncompagni, was Pope of the Catholic Church from 13 May 1572 to his death in 1585. He is best known for commissioning and being the namesake for the Gregorian calendar, which remains the internationally accepted civil calendar to this day.
Upon the death of Pope Pius V, the conclave chose Cardinal Boncompagni, who assumed the name of Gregory XIII in homage to the great reforming Pope, Gregory I (590 - 604), surnamed the Great. It was a very brief conclave, lasting less than 24 hours. Many historians have attributed this to the influence and backing of the Spanish King. Gregory XIII's character seemed to be perfect for the needs of the church at the time. Unlike some of his predecessors, he was to lead a faultless personal life, becoming a model for his simplicity of life. Additionally, his legal brilliance and management abilities meant that he was able to respond and deal with major problems quickly and decisively, although not always successfully.