Catherine (or Katharine or Katherine) (~1350 - 1403) was the daughter of Payne (or Paen) de Roet (or Rouet or Roelt) a Flemish herald from Hainault who was knighted just before dying in the wars, leaving Catherine and her older sister Philippa, as well as a brother, Walter, and eldest sister, Isabel/Elizabeth de Ruet,( who died chanoinness of the convent of St. Waudru's, Mons, ca. 1366) . Born in about 1350, in about 1366 Catherine married Hugh Swynford or Synford, an English knight from the manor of Kettlethorpe in Lincolnshire, and bore him at least two children (Blanch, Thomas and likely the Margaret Swynford who was nominated a nun at the prestigious Barking Abbey by the command of Richard II in 1377) before he, too, died in the European wars. She then became attached to the household of John of Gaunt, Duke of Lancaster, ostensibly as governess to his two daughters (the sisters of the future Henry IV of England) by his first wife Blanche, but eventually she became his official mistress. Catherine's sister Philippa married the poet Geoffrey Chaucer, whose poem The Book of the Duchess commemorated Blanche's death in about 1369.
Long after the death of his second wife Constance (or Constanza) of Castile, John and Catherine married in January 1396, three years before he died. The four children Catherine had borne John of Gaunt had been given the surname "Beaufort" and were already adults when they were legitimized (but barred from inheriting the throne by a clause inserted by half-brother Henry IV well into the latter's reign) in 1390: John Earl of Somerset, Henry Cardinal Beaufort, Thomas Beaufort Duke of Exeter, and Joan Countess of Westmoreland.
The coat of arms designed for Catherine was three gold Catherine wheels ("roet" means "wheel") on a red background.
Her son John was the great-grandfather of Henry VII of England; her daughter Joan was the grandmother of Edward IV of England and Richard III of England, whom Henry VII defeated to take the throne (before marrying the daughter of Edward IV, and their son became Henry VIII). Her step-son became Henry IV of England by deposing Richard II of England (who was imprisoned and died shortly thereafter, in Pontefract Castle, where Catherine's son Thomas Swynford was constable, and he was said to have starved Richard to death for his step-brother); her step-daughter, John and Constance's daughter Catherine (or Catalina), was the great-grandmother of Catherine of Aragon, the first wife of Henry VIII of England and mother of Mary I of England.
Catherine survived John by only four years, dying on 10 May 1403. (Since she was then dowager Duchess of Lancaster, there was a record of the exact day, as there was not for her birth, when she was a nobody.) Her tomb, and that of her daughter Joan Beaufort, are under a carved-stone canopy in the sanctuary of Lincoln Cathedral, but their remains are no longer in them, because the tombs were despoiled in 1644, during the English Civil War, by the Roundheads.
Katherine Swynford is the subject of Anya Seton's novel Katherine (©1954).