Who was Pope Gregory XIII?

A:

Pope Gregory XIII, born Ugo Boncompagni, was leader of the Catholic Church from 1572 to 1585. His greatest accomplishment was to commission the Gregorian calendar, which is the standard calendar used around the world today.

Gregory was certainly no saint. He had an illegitimate son before he took holy orders, and his previous life had been "rather worldly". While apologists frequently claim that Gregory was above nepotism, the opposite is true. One of his first acts as Pope was to appoint his son a Cardinal at age 24 and prefect of Castel Sant'Angelo. Pope Gregory VIII also made him General Governor of the Papal Army. In 1576 he appointed his son Governor of Fermo. Gregory had numerous nephews, and created two of them as cardinals

Upon hearing of the wholesale slaughter of the French Huguenots, known as St. Bartholomew's massacre, Pope Gregory had a medal struck to celebrate the event, and celebrated the massacre at mass.