Jan Hus

Jan Hus, sometimes anglicized as John Hus or John Huss, and referred to in historical texts as Iohannes Hus or Johannes Huss, was a Czech theologian and philosopher who became a Church reformer and the inspiration of Hussitism, a key predecessor to Protestantism, and a seminal figure in the Bohemian Reformation. Hus is considered to be the first Church reformer, even though some designate the theorist John Wycliffe. His teachings had a strong influence, most immediately in the approval of a reformed Bohemian religious denomination and, over a century later, on Martin Luther.
After being ordained as a Catholic priest, Hus began to preach in Prague. He opposed many aspects of the Catholic Church in Bohemia, such as its views on ecclesiology, simony, the Eucharist, and other theological topics. Hus was a master, dean and rector at the Charles University in Prague between 1409 and 1410.
Alexander V issued a Papal bull that excommunicated Hus; however, it was not enforced, and Hus continued to preach. Hus then spoke out against Alexander V's successor, Antipope John XXIII, for his selling of indulgences.