and "Partium"). John Sigismund initiated a series of theological debates among the representatives of the concurring theological schools of the Reformation in the 1560s. He converted from Catholicism to Lutheranism in 1562 and from Lutheranism to Calvinism in 1564. Around five years later, accepting the Anti-Trinitarian views of his physician, Giorgio Biandrata and court preacher Ferenc Dávid, he became the only Unitarian monarch in history. In 1568, the Diet passed the Edict of Torda (now Turda in Romania), which emphasized that "faith is a gift of God" and prohibited the persecution of people for religious reasons. The edict expanded the limits of freedom of religion beyond the standards of late 16th-century Europe. John Sigismund abandoned the title "elected king of Hungary" in the Treaty of Speyer in 1570. Thereafter, he styled himself "Prince of Transylvania and Lord of Parts of the Kingdom of Hungary". He died childless. The Catholic Stephen Báthory succeeded him. Family John Sigismund's father, John Zápolya, was the wealthiest Hungarian lord in the early . After the Ottoman Sultan, Suleiman the Magnificent, inflicted a crushing defeat on the Hungarian army in the Battle of Mohács, the majority of the noblemen elected John Zápolya king in 1526. However, a group of influential lords proclaimed Ferdinand I, Archduke of Austria, king in the same year. Hungary fell into a civil war that lasted for decades. John paid homage to Suleiman at Mohács in 1529 to secure Ottoman support against Ferdinand. However, neither John nor Ferdinand could win control of the whole country during the next years. To conclude the civil war, the two kings' envoys signed the Treaty of Várad on 24February 1538, which confirmed both kings' right to retain the lands that they held. John, who was childless, also acknowledged Ferdinand's right to take control of his realm (the central and eastern part of the Kingdom of Hungary) after his death. John also stipulated, if he fathered a son, his son would inherit his ancestral domains. Ferdinand, however, proved unable to protect John's realm against an Ottoman invasion. At age 52 John married Isabella Jagiellon, the 22-year-old daughter of Sigismund I the Old, King of Poland, on 2March 1539. The humanist scholars Paolo Giovio and Antun Vrančić emphasized that Isabella was one of the most educated women of their age. John Sigismund was born in Buda on 7 July 1540. On learning of his birth, his father, who