John of Gaunt, 1st Duke of Lancaster, KG (6 March 1340 – 3 February 1399), nobleman, soldier, and statesman, was the third of five surviving sons of King Edward III of England. As a prince of the royal family, he was an influential figure in the reigns of his father and nephew, Richard II, and fought as a military commander in the Hundred Years' War. His name was derived from the fact that he was born in Ghent which then was rendered in English as Gaunt. When he became unpopular later in life, scurrilous rumours and lampoons circulated that he was actually the son of a Ghent butcher, perhaps because Edward III was not present at the birth. This story always drove him to fury.
Owing to his royal origin, advantageous marriages and some generous land grants, he was one of the richest and most influential men of his era. His career, however, went through a time of difficulty for England, amidst military reverses in the ongoing Hundred Years' War with France and internal problems at home. His influence in national affairs, thanks to the incapacity of his father and brother, made him the focus of much popular discontent. He made an abortive attempt to enforce a claim to the Crown of Castile that came courtesy of his second wife, and for a time styled himself as King of Castile.
John exercised great influence over the English throne during the minority King Richard II, and the ensuing periods of political strife. The king came into conflict with Gaunt's son and heir, Henry Bolingbroke, among others. John acted as a mediator between Richard and his opponents, but following his death in 1399, his estates and titles were declared forfeit to the crown, and his son, now disinherited, was branded a traitor and exiled. Henry Bolingbroke returned from exile shortly after to reclaim his inheritance, and deposed Richard. He reigned as King Henry IV of England (1399–1413), the first of the descendants of John of Gaunt to hold the English throne.
As Duke of Lancaster, Gaunt is seen as the founder of the House of Lancaster, whose male heirs would rule England from 1399 until the time of the Wars of the Roses, when the English crown was disputed with the House of York (formed by the descendants of his younger brother Edmund, Duke of York). Gaunt also fathered five children outside marriage (one early in life by a lady-in-waiting to his mother), four of which (by Katherine Swynford, Gaunt's long-term mistress and third wife) were later legitimized by royal and papal decrees. Through these offspring, surnamed "Beaufort", he is ancestor to all Scottish monarchs beginning in 1437, and of all English monarchs of the houses of York and Tudor. Thus, all English kings during the Wars of the Roses were descended from him, making him an ancestor of all subsequent kings of England. Through his eldest daughter, all Portuguese monarchs starting in 1433 descend from him. Through his other daughter, he has among his descendants all monarchs of Castile from 1406, and subsequently those of a united Spain. Finally, John of Gaunt is also an ancestor of the Habsburg rulers who would reign in Spain and much of central Europe.
John was the third surviving son of King Edward III of England. His first wife, Blanche of Lancaster, was also his third cousin; both were great-great-grandchildren of King Henry III. They married in 1359 at Reading Abbey as a part of the efforts of Edward III to arrange matches for his sons with wealthy heiresses. Upon the death of his father-in-law, the 1st Duke of Lancaster, in 1361, John received half his lands, the title "Earl of Lancaster", and distinction as the greatest landowner in the north of England as heir of the Palatinate of Lancaster. He also became the 14th Baron of Halton and 11th Lord of Bowland. John inherited the rest of the Lancaster property when Blanche's sister Maud, Countess of Leicester (married to William V, Count of Hainaut), died without issue on 10 April 1362.
John received the title "Duke of Lancaster" from his father on 13 November 1362. By then well established, he owned at least thirty castles and estates across England and France and maintained a household comparable in scale and organisation to that of a monarch. He owned land in almost every county in England, a patrimony that produced a net income of between £8,000 and £10,000 a year.
After the death in 1376 of his older brother Edward of Woodstock (also known as the "Black Prince"), John of Gaunt contrived to protect the religious reformer John Wycliffe, possibly to counteract the growing secular power of the church. However, John's ascendancy to political power coincided with widespread resentment of his influence. At a time when English forces encountered setbacks in the Hundred Years' War against France, and Edward III's rule was becoming unpopular due to high taxation and his affair with Alice Perrers, political opinion closely associated the Duke of Lancaster with the failing government of the 1370s. Furthermore, while King Edward and the Prince of Wales were popular heroes due to their successes on the battlefield, John of Gaunt had not won equivalent military renown that could have bolstered his reputation. Although he fought in the Battle of Nájera (1367), for example, his later military projects proved unsuccessful.