Geoffrey Chaucer (/ˈdʒɛfri/ /ˈtʃɔːsər/; JEF-ree CHAW-sər; c. 1343 – 25 October 1400) was an English poet, writer and civil servant best known for The Canterbury Tales. He has been called the 'father of English literature', or alternatively, the 'father of English poetry'. He was the first writer to be buried in what has since become Poets' Corner in Westminster Abbey.

Chaucer also gained fame as a philosopher and astronomer, composing the scientific A Treatise on the Astrolabe for his ten-year-old son, Lewis. He maintained a career in public service as a bureaucrat, courtier, diplomat and member of the Parliament of England, having been elected as shire knight for Kent.

Amongst his other works are The Book of the Duchess, The House of Fame, The Legend of Good Women, Troilus and Criseyde, and Parlement of Foules. A prolific writer, Chaucer has been seen as crucial in legitimising the literary use of Middle English at a time when the dominant literary languages in England were still Anglo-Norman French and Latin. His contemporary Thomas Hoccleve hailed him as "the firste fyndere of our fair langage" (i.e., the first one capable of finding poetic matter in English). Almost two thousand English words are first attested in Chaucerian manuscripts.

Geoffrey Chaucer was born in London, most likely in the early 1340s (by some accounts, including his monument, he was born in 1343), though the precise date and location remain unknown. The Chaucer family offers an extraordinary example of upward mobility. His great-grandfather Andrew de Chaucer was a tavern keeper, his grandfather Robert Malyn le Chaucer worked as a purveyor of wines, and his father, John Chaucer, rose to become an important wine merchant with a royal appointment. Several previous generations of Geoffrey Chaucer's family had been vintners and merchants in Ipswich. His surname is derived from the French chaucier, once thought to mean 'shoemaker', but now known to refer to a maker of chausses (leggings).

In 1324 his father, John Chaucer, was kidnapped by an aunt in the hope of marrying the twelve-year-old to her daughter in an attempt to keep the Ipswich property in the family. The aunt was imprisoned and fined £250, now equivalent to about £200,000, suggesting the family was financially secure.

John Chaucer married Agnes Copton, who inherited properties in 1349, including 24 shops in London, from her uncle Hamo de Copton, who is described in a will dated 3 April 1354 and listed in the City Hustings Roll as 'moneyer', apparently employed at the Tower of London. In the City Hustings Roll 110, 5, Ric II, dated June 1380, Chaucer refers to himself as me Galfridum Chaucer, filium Johannis Chaucer, Vinetarii, Londonie, Latin for: "I, Geoffrey Chaucer, son of the vintner John Chaucer, London".

Although records of the lives of Chaucer's contemporaries William Langland and the Gawain Poet are practically non-existent, Chaucer was a public servant whose official life was very well documented. Nearly 500 written items testify to his career. The first of the 'Chaucer Life Records' appears in 1357 in the household accounts of Elizabeth de Burgh, the Countess of Ulster, when he became the noblewoman's page through his father's connections, a common medieval form of apprenticeship for boys into knighthood or prestige appointments. De Burgh was married to Lionel of Antwerp, 1st Duke of Clarence, the second surviving son of Edward III; this position brought the teenage Chaucer into the close court circle, where he was to remain for the rest of his life. He was also employed as a courtier, a diplomat and a civil servant, as well as working for the king from 1389 to 1391 as Clerk of the King's Works.

In 1359, in the early stages of the Hundred Years' War, Edward invaded France. Chaucer travelled with Lionel of Antwerp, Elizabeth's husband, as part of the English army. In 1360 he was captured during the siege of Reims. The king paid £16 for his ransom, equivalent to £14,557 in 2023, and Chaucer was released.