October 31, 2017 marks the 500th Anniversary of the date on which Martin Luther submitted a document to the Roman Catholic Church which would come to be known as the 95 Theses, primarily dealing with the protest that Luther, a Monk and Professor, was making against the churches' sale of 'indulgences'... Essentially allowing people to make large donations to the church in exchange for a 'get out of jail free' card in regard to major sins committed by the donor, supposedly so they wouldn't have to answer for them in Heaven.
Some accounts state that Luther simply wrote to the Bishop of his local church, others claim that he walked up to the church and nailed the document to the front door.
Either way, the short and long term effects of this on the Catholic Church were profound. Interestingly, this event also coincided with the second of the Ten Jubilees