Catherine (or Katharine or Katherine), 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 younger sister Philippa orphans. Born in about 1350, in about 1366 Catherine married Hugh Swynford, an English knight from the manor of Kettlethorpe in Lincolnshire, and bore him at least two children (Blanchette, Thomas, and maybe Margaret) before he, too, died in the European wars. She then became attached to the household of John Duke of Gaunt, ostensibly as governess to his two daughters (the sisters of the future Henry IV of England) by his first wife Blanche, but eventually as his official mistress. Catherine's sister Philippa married the poetGeoffrey 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, 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): John Beaufort Earl of Somerset, Henry Cardinal Beaufort, Thomas Beaufort Duke of Exeter, and Joan Beaufort 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 Beaufort was the grandfather of Henry VII of England; her daughter Joan Beaufort 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; her step-daughter, John and Constance's daughter Catherine (or Catalina), was the 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. 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.