Answer: Pope Boniface VIII began the tradition of the Holy Year, known as a Jubilee, in 1300. He intended that a Holy Year would be celebrated every 100 years, but Pope Paul III, in 1470, changed to cycle to every 25 years. Pope Frances made an exception and proclaimed 2016 a special Holy Year.

See:
 •  John Laino, Pope Boniface VIII and the Holy Year Vatican Notes Volume 51, Issue: 2, September 2002, Page 7


Pope Boniface VIII
Scott # 1065 (1998)