Geoffrey Chaucer (c. 1343 – 25 October 1400), known as the Father of English literature, is widely considered the greatest English poet of the Middle Ages and was the first poet to have been buried in Poet's Corner of Westminster Abbey. While he achieved fame during his lifetime as an author, philosopher, alchemist and astronomer, composing a scientific treatise on the astrolabe for his ten year-old son Lewis, Chaucer also maintained an active career in the civil service as a bureaucrat, courtier and diplomat. Among his many works, which include The Book of the Duchess, the House of Fame, the Legend of Good Women and Troilus and Criseyde, he is best known today for The Canterbury Tales. Chaucer is a crucial figure in developing the legitimacy of the vernacular, Middle English, at a time when the dominant literary languages in England were French and Latin.