John Sigismund Zápolya (1540–1571), King of Hungary (as John II) and the first Prince of Transylvania, the only Unitarian monarch in history.
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. (Note: Not to be confused with modern Unitarian Universalism. The original Unitarian movement, was very Christian in its origin, beliefs and preaching). 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 religionbeyond 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.