Middle-earth Legendarium

The legendarium (also called Tolkien Mythology) is the corpus of connected, fantastical stories imagined and written by J.R.R. Tolkien, making up the history of Arda, and the entire extensive background to The Lord of the Rings. This legendarium was developed in evolving, complex stages over almost six decades of Tolkien's life. Before the induction of The Hobbit into the legendarium, the majority of these writings, revealing a vast ancient and First Age history of Arda, were named the "Silmarillion". These tales and their settings changed through many stages of development throughout Tolkien's life, and the final versions of many of them were selected and published together as The Silmarillion by Tolkien's son, Christopher, after his death. (https://lotr.fandom.com/wiki/Legendarium)