There were no printed books in Chaucer's era, and there was little contact between different parts of Britain, so the English spoken in different parts was very different. Furthermore, at that time, the court language was French and the academic language was Latin. Chaucer was the first court writer to write in English. Living in London, he naturally uses English from counties in central England, rather than dialects in northern or southern England. His works have made great contributions to the formation of modern English.
When Chaucer was young, he translated part of the immortal French love poem The Legend of the Rose into English. His first work was The Duchess's Book. Troy Lars and Clayside, based on Boccaccio's story, shows Chaucer's truly great poetic talent. His last, longest and most famous work is Canterbury Tales. Until Shakespeare's time, his works dominated English poetry.