Here are short descriptions of the main historic figures and terms referred to in A Mighty Fortress and its new Prologue.
Being a bit familiar with them in advance will definitely help you to appreciate the events more thoroughly.
HISTORIC PEOPLE AND TERMS FOR YOU TO KNOW:
John Wycliffe (ca 1320 to 1384): known as the “Morning Star” of the English Reformation, an Oxford seminary professor who publicly criticized the decadence of the clergy and the luxurious excess of the Church. He supported rendering the Scriptures into the language of the common people, and supervised a translation of the Bible from the Vulgate into Middle English. He died of a stroke in 1384. He was declared a heretic by the Catholic Church in 1415, and his remains were exhumed, burned, and cast into a river.