Celibacy has been mandatory for popes and clergy for nearly 900 years, since the Second Lateran Council took place in 1139. Before that, several heads of the Catholic Church were family men: Seven popes were married before entering the priesthood, and at least 15 had children. 

Those married pontiffs included the very first pope, St. Peter, as well as St. Felix III (who served 483-492), St. Hormisdas (514-523), St. Agatho (678-681), Adrian II (867-872), John XVII (1003), and Clement IV (1265-1268).

Even before the Second Lateran Council, though, there were plenty of rules and regulations regarding the personal lives of Catholic leaders. The Council of Elvira in 306 decreed that a priest who sleeps with his wife the night before will be defrocked, while the 325 Council of Nicaea forbade priests from living with unmarried women. 

In 385, popes were forbidden from sleeping with their wives, and in 1045 Benedict IX (who held the papacy three tumultuous times) resigned — ostensibly in order to get married, though the fact that he sold the office to his godfather complicates the story. Several popes also had children outside of marriage, including Leo XII, Clement VII, and Innocent VIII, who was the first to openly acknowledge doing so.