Thomas Beaufort, 1st Duke of Exeter KG (c. 1377 – c. 31 December 1426) was an English military commander during the Hundred Years' War, and briefly Chancellor of England. He was the third of the four born to John of Gaunt, Duke of Lancaster, and his mistress Katherine Swynford. To overcome their problematic parentage, his parents were married in 1396, and he and his siblings were legitimated on two separate occasions, in 1390 and again in 1397.