John Sigismund Zápolya

Born 7 July 1540, John Sigismund was the only son of John I, King of Hungary, and Isabella of Poland. His father died shortly after his birth, bequeathing him a realm already contested by Ferdinand I of Habsburg under a 1538 treaty meant to reunite Hungary. Elected king as an infant but never crowned, he watched Suleiman's armies take Buda in 1541 while his mother retained the lands east of the Tisza. His father's treasurer, George Martinuzzi, forced Isabella to renounce the realm in 1551 for two Silesian duchies and 140,000 florins, sending mother and son into Polish exile. The Transylvanian Diet recalled them in 1556 at Suleiman's urging; Isabella ruled until her death in 1559, after which John Sigismund faced rebellion from the Székely people and the lord Melchior Balassa while Ferdinand seized most counties outside Transylvania. He crushed the Székely uprising, paid homage to Suleiman at Zemun in 1566, and secured his eastern territories through the 1568 Treaty of Adrianople. He converted from Catholicism to Lutheranism in 1562, to Calvinism in 1564, and around 1569 embraced the Anti-Trinitarian views of his physician Giorgio Biandrata, becoming the only Uni