John of Gaunt
John of Gaunt (1340–99), duke of Lancaster, fourth son of Edward III of England. Through marriage to his cousin Blanche, he became the duke of Lancaster. (Their eldest son became King Henry IV.) A commander in France under his brother, Edward the Black Prince, during the Hundred Years War, he married again, in 1371. Through his second wife, Constance of Castile, he gained a claim to the kingship of Castile and Léon. He ruled England for his senile father when the Black Prince was taken ill and his nephew, Richard II, was too young to assume leadership. His economic policies made him unpopular in many quarters, as did his unsuccessful campaigns (1386–88) to claim the Castilian throne. He remained influential during Richard II's reign, helping to effect peace between Richard and his barons. In 1396 he married Catherine Swynford, his third wife. They were ancestors of the Tudors.