John of Gaunt

Born in Ghent in 1340, the fourth son of Edward III, John of Gaunt spent his early career fighting in France and Spain during the Hundred Years' War. His second marriage to Constance of Castile brought a claim to that throne, which he tried and failed to enforce, styling himself King of Castile for a time. When his elder brother Edward the Black Prince fell ill, Gaunt assumed control of much of the English government, becoming one of the most powerful men in the realm - but also deeply unpopular amid military setbacks abroad and political divisions at home. He helped broker the 1386 Anglo-Portuguese alliance through his daughter Philippa's marriage to John I, a treaty still standing today. During the minority of his nephew Richard II, Gaunt mediated between king and rebels, even as his own son Henry Bolingbroke joined the opposition. When Gaunt died in 1399, Richard declared the Lancastrian estates forfeit and exiled Henry - who returned with an army, deposed the king, and took the throne as Henry IV. Every English monarch since descends from Gaunt, whether through his legitimate line or through the Beauforts, his children by longtime mistress Katherine Swynford