Titles:
Knight of the Garter
Earl of Richmond (1342 cr)  
Earl of Lancaster (1361 m - 1st)  
Earl of Derby (1362 m - 1st)  
Earl of Leicester (1362 m - 1st)  
Earl of Lincoln (1362 m - 1st)  
Duke of Lancaster (1362 cr - 1st)  
Duke of Aquitaine (1389 cr)

John is sometimes given the title "King of Castile and Leon", a reference to his marriage to Constance of Castile.

John of Gaunt, Duke of Lancaster (June 24, 1340 – February 3, 1399) was the third surviving son of King Edward III of England and Philippa of Hainault. He gained his name "John of Gaunt" because he was born at Ghent in 1340. The fabulously wealthy Gaunt exercised tremendous influence over the throne during the minority reign of his nephew, Richard II, and during the ensuing periods of political strife, but took care not to be openly associated with opponents of the King.

John of Gaunt's legitimate male heirs, the Lancasters, included Kings Henry IV, Henry V, and Henry VI. John of Gaunt's illegitimate descendants, the Beauforts, later married into the House of Tudor, which ascended to the throne in the person of Henry VII. In addition, Gaunt's legitimate descendants included his daughters Philippa of Lancaster, Queen consort of John I of Portugal and mother of King Edward of Portugal, Elizabeth, Duchess of Exeter, the mother of John Holland, 2nd Duke of Exeter, and Katherine of Lancaster, Queen consort of Henry III of Castile, a grand-daughter of Peter I of Castile and the mother of John II of Castile.

When John of Gaunt died in 1399, his estates were declared forfeit to the crown, as Richard II had exiled John's less diplomatic heir, Henry Bolingbroke, in 1398. Bolingbroke returned and deposed the unpopular Richard, to reign as King Henry IV of England (1399–1413), the first of the descendants of John of Gaunt to hold the throne of England.

Because John's romance with Katherine Swynford has been such a distinctive part of his biography, it is easy to overlook the devotion he apparently felt for his first wife, Blanche. After her death, he established a number of chantries to say masses for her soul, and funded an expensive yearly memorial service. John's great biographer, Sidney Armitage-Smith reports that there is no evidence that John was ever unfaithful to Blanche.

In 1377, King Edward III changed the status of John's county of Lancaster, making him the Earl Palatinate, as John's late father-in-law, Henry of Grosmont had been. This had significant implications for the county as a revenue unit, and formed the basis on which John's son Henry IV sectioned off the Duchy of Lancaster to keep its fortune separate from that of the crown. Over the years, the set of transactions has had enormous financial implications for the holder of the duchy (its revenues, for instance, funded much of the Lancastrian war effort in the Wars of the Roses). The duchy's bondsmen were in technical thrall long after serfdom was abolished in England, and Elizabeth I manumitted a great number of them.

Among John's lesser-known achievements: some historians credit him with introducing morris dancers to England from Spain.

According to some sources, John died at Leicester Castle.

John is depicted in a stained-glass window in the chapel of All Soul's College, University of Oxford. The window apparently shows him late in life, because his hair and beard are almost white.

In his lifetime, nobody called him John of Gaunt after his very early childhood; the name only became popular 200 years later after Shakespeare used it in Richard II.

A character in Shakespeare's play Richard II, who says one of the playwright's most famous lines: "This royal throne of kings, this sceptr'd isle, This earth of majesty, this seat of Mars, This other Eden, demi-paradise, This fortress built by Nature for herself Against infection and the hand of war, This happy breed of men, this little world, This precious stone set in the silver sea, Which serves it in the office of a wall, Or as a moat defensive to a house, Against the envy of less happier lands; This blessed plot, this earth, this realm, this England..." Richard II Act 2, scene 1

In Richard II, Shakespeare assigns John a number of good speeches. After John's son Henry is banished, John gives him some advice: "GAUNT. Call it a travel that thou tak'st for pleasure. BOLINGBROKE. My heart will sigh when I miscall it so, Which finds it an enforced pilgrimage.... GAUNT. All places that the eye of heaven visits Are to a wise man ports and happy havens. Teach thy necessity to reason thus: There is no virtue like necessity." Richard II Act 1, scene 3

As Gaunt is dying, he admonishes his nephew, King Richard: "Why, cousin, wert thou regent of the world, It were a shame to let this land by lease; But for thy world enjoying but this land, Is it not more than shame to shame it so? Landlord of England art thou now, not King." Richard II Act 2, scene 1