J. R. R. Tolkien (1892-1973) is best known for his literary works, especially for The Hobbit and The Lord of the Rings. These have been objects of studies by some disciplines such as philosophy, psychology, theology or literature. However, until a few years ago there were hardly any scientific works on the artificial languages that led to the appearance of these stories. This paper studies Tolkien's love for languages and his work as inventor of artificial linguistic systems. Secondly, we show how this author maintained his activity as a creator of languagesin secret and how he revealed this hidden office before an audience of scholars and philologists. Finally, this analyzes some of the principles of his linguistic invention and how influences the academic context of the early twentieth century. This study allows us to conclude that these linguistic designs, with their rules and exceptions, represent the mirror in which the changing linguistic ideas of a passionate of language are reflected.