John Sigismund Zápolya or Szapolyai (; 7 July 1540 – 14 March 1571) was King of Hungary as John II from 1540 to 1551 and from 1556 to 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. JohnI ruled parts of the Kingdom of Hungary with the support of the Ottoman Sultan Suleiman; the remaining areas were ruled by Ferdinand I of Habsburg, who also ruled Austria and Bohemia. The two kings concluded a peace treaty in 1538 acknowledging Ferdinand's right to reunite Hungary after JohnI's death, though shortly after John Sigismund's birth, and on his deathbed, JohnI bequeathed his realm to his son. The late king's staunchest supporters elected the infant John Sigismund king, but he was not crowned with the Holy Crown of Hungary.