Answer
Isabella Jagiellon, the wife of John Zápolya, played a significant role in his reign as King of Hungary. She was the daughter of King Sigismund I of Poland and Bona Sforza, and her marriage to Zápolya in 1539 strengthened his claim to the Hungarian throne. Isabella was a skilled diplomat and a strong supporter of her husband, and she continued to rule Hungary as regent after his death in 1540.