John Sigismund Zápolya or Szapolyai (; 7 July 1540–14 March 1571) was King of Hungary (as John II) from 1540 to 1551, and again between 1556 and 1570, and the first Prince of Transylvania from 1570 to his death. He was the only son of John I, King of Hungary, and Isabella of Poland. John I had only been able to preserve parts of the Kingdom of Hungary against his opponent, Ferdinand I, with the support of the Ottoman Sultan Suleiman the Magnificent. Before John Sigismund's birth, John and Ferdinand concluded a peace treaty which acknowledged Ferdinand's right to reunite the whole kingdom after John's death. However, John bequeathed his realm to John Sigismund on his deathbed, only two weeks after John Sigismund's birth. His father's staunchest supporters elected the infant John Sigismund king, but he was never crowned with the Holy Crown of Hungary.