The Silmarillion

No, The Silmarillion is not required reading before The Lord of the Rings and is actually much denser and more challenging for most readers. It functions more as a mythological pre-history covering the creation of Middle-earth and the First Age, while The Lord of the Rings takes place much later in the Third Age.

The book is written in an elevated, almost biblical style that mirrors ancient mythological texts rather than the narrative prose of The Lord of the Rings. It spans thousands of years of fictional history, involves hundreds of characters and place names, and was compiled posthumously by Christopher Tolkien from his father's unfinished manuscripts.

Fëanor was a Noldorin elf who crafted three perfect jewels called the Silmarils, which captured the light of the Two Trees of Valinor. When the dark lord Morgoth stole the Silmarils, Fëanor led a rebellion of elves back to Middle-earth to wage war against him, setting in motion much of the tragedy of the First Age.

J.R.R. Tolkien worked on the material that became The Silmarillion throughout much of his life, but he never completed it before his death in 1973. His son Christopher Tolkien edited the manuscripts and published the book in 1977.