He is best known as the father of modern high fantasy fiction with his fantasy novels, The Hobbit and The Lord of the Rings Trilogy. He also did much critical work on Beowulf and Sir Gawain and the Green Knight. He was one of the members of the literary discussion group The Inklings, and very close friends with C. S. Lewis.
Tolkien created numerous artificial languages (among which the most famous are the two Elvish languages from Lord of the Rings, Quenya and Sindarin). Tolkien was familiar with the artificial language, Esperanto, which he learned at 17 years of age. Though he did not claim to be an Esperantist, he was quoted as promoting its use.
J. R. R. Tolkien was born in Bloemfontein, South Africa. His father died when he was a young child. His mother converted to Catholicism, despite the vehement protests of her family. She later died when he was a young teenager due to diabetes, but he felt for the rest of his life that she was a martyr for her faith; this had a profound affect on his own Catholic beliefs. During his subsequent orphanage[?], he met and fell in love with Edith Bratt[?] (later to serve as his model for Luthien). Despite many obstacles, he was able to marry her, the first and truest love of his life. Tolkien served in the British Army during World War I. He served in the Lancashire Fusiliers[?], the most-decorated British unit in the war. He saw a number of his fellow servicemen, as well as several of his closest friends, lose their lives. He himself ended up in a military hospital, suffering from trench fever. It was during his recovery that he began to write an invented series of fairy tales based upon his studies of mythology and folklore that he called 'The Book of Lost Tales.' Scholars of his work say that the war influenced his writings; that he saw fantasy as a way to escape from the harsh reality of factories, machines, guns and bombs of the 20th century.
Tolkien never expected his fictional stories to be embraced by the public. Through the intercession of a former student, he published a book he had written for his own children called The Hobbit (1937). Though intended for children, the book was read by adults as well, and it was popular enough for the publisher (Allen & Unwin) to convince Tolkien to work upon a sequel. This prompted him to create his most famous work, the epic three-volume novel The Lord of the Rings (1954-55), which the Encyclopaedia Britannica has called "richly inventive"  (http://search.britannica.com/search?query=John%20R.%20R.+Tolkien). The writing of this epic saga took nearly ten years, during which time he received the constant support of the Inklings and his closest friend, C. S. Lewis. While the Lord of the Rings was immensely popular with many students in the 1960s, and has remained highly popular since, many scholars (particularly those working in the field of Norse mythology), aware of Tolkien's sources, consider the work highly derivative. Tolkien at first thought that The Lord of the Rings would be another children's book like The Hobbit, but it quickly grew darker and more serious in the writing. Though a direct sequel to The Hobbit, it was intended for a much older audience, drawing upon the immense back-story of Middle-earth that he had constructed and that eventually saw publication in the The Silmarillion and in other posthumous volumes.
The Lord of the Rings was, judged both by sales and surveys of readers, one of the most popular works of fiction of the twentieth century. The influence of Tolkien weighs heavily on the fantasy genre that grew up after the success of The Lord of the Rings, which has been made into three films.
Work published in JRRT's lifetime:
Posthumous non-Middle-earth material
Tolkien continued to work upon the history of Middle-earth until his death. His son Christopher Tolkien, with assistance from fantasy writer Guy Gavriel Kay, organised some of this material into one volume, published as The Silmarillion in 1977.
Christopher Tolkien continued over subsequent years to publish lots of background material on the creation of Middle-earth, beginning with Unfinished Tales (1980), The Letters of J. R. R. Tolkien[?] (1981), and an essay collection, The Monsters and the Critics[?] (1983), and continuing with:
The History of Middle-Earth series