John of Gaunt was the fourth son of Edward III, born in Ghent in 1340. He married Blanche, the heiress of the duchy of Lancaster, in 1359 and was himself created Duke of Lancaster in 1362. Widowed in 1369, John married Constance, daughter of Pedro the Cruel of Castile, and in 1372 assumed the title of King of Castile. In 1387, he resigned all claims in favor of his daughter, Catherine. John was influential during the reign of Richard II and tried to promote peace between the king and his nobles. His children by Catherine Swynford, known as the Beauforts, were legitimized by Richard II and figured prominently in English affairs in the next century. John's eldest son, Henry Bolingbroke, became king as Henry IV, the first king of the House of Lancaster.