Geoffrey Chauser (1340-1400) was the most outstanding figure of the time and very often he is described as the father of the literary language.

Chaucer was born in London and had the most varied experience as student, courtier, official, and member of Parliament. His early works were more or less imitative of other authors — Latin, French or Italian . He never wrote in any other language than English. The culmination of Chaucer's work as a poet is his great unfinished collection of stories The Canterbury Tales.

The Canterbury Tales.
The Prologue of this poem, the masterpiece of English poetry, describes how the poet found himself at the Tabard Inn, in Southwark, bound on a pilgrimage to the shrine of St. Thomas Becket at Canterbury. There he met twenty-nine other pilgrims, who, at the suggestion of the host, agreed to liven up the journey by story-telling. Chaucer lived to write only twenty-four stories out of the intendea sixty, but in the Prologue he managed to give a most vivid picture of contemporary England: he presented in the pilgrims a gallery of life-like portraits taken from all walks of life. In social position they range from knight and prioress to drunken cook and humble plowman — a doctor, a lawyer, a monk, a sailor, a carpenter, an Oxford scholar and many others. These people are shown as they appear on the road, with their distinctive dress and features, and with a bit of their personal history. Even in their choice of tales they unconsciously reveal themselves, the stories being in harmony with the character of the .narrators (e.g. the knight relates a story of chivalry).
Chaucer wrote in a dialect which in the main coincided with that used in documents produced in London shortly before his time and for a long time after.In the history of English literature, Chaucer is considered the introducer of continental accentual-syllabic metre as an alternative to the alliterative Anglo-Saxon metre. He was one of the first English poets to use the five-stress line, the iambic pentameter, in his work. Although he did not really create the literary language, as a poet of outstanding talent he made better use of it than his contemporaries and set up a pattern to be followed in the 15th c. His poems were copied so many times that over sixty manuscripts of THE CANTERBURY TALES have survived to this day. His books were among the first to be printed, a hundred years after their composition.
Chaucer's literary language, based on the mixed (largely East Midland) London dialect is known as classical ME; in the 15th and 16th c. it became the basis of the national literary English language.