If you’ve read the Lord of the Rings books, you’ll have noticed that Tolkien created a deep and extensive mythological backstory for his world. If you’ve read The Silmarillion, you saw this mythology play out on the page, from the creation of the whole universe and the planet of Arda, up through the end of the Third Age, which is the end of the LotR story.
Tolkien’s mythology draws a lot from both Catholicism and ancient Norse religion. As he was a follower of the former and a scholar of the latter, it’s been argued that the story of Arda was his attempt to reconcile the two. Whether this is true or not, it’s undeniable that Tolkein was inspired by the two belief systems when he created the history of Middle-Earth.
Elves in Norse mythology are very similar to those in the Tolkien’s stories: tall, graceful, powerful, noble, and immortal, but inferior to the gods. The gods of Norse mythology, known as the Aesir or the Vanir, are similar to the Valar or the Maiar, the angelic beings who assisted the god of Middle-earth, Iluvatar, with the creation of the world.
Rings of Power are also featured widely in Norse mythology. The greatest of these was the extraordinarily powerful Draupnir, a ring that belonged to Odin. Draupnir granted the wearer rule over the Nine Worlds of Norse mythology. The greatest of the Norse Elvish smiths forged Draupnir, which was imbued with all of Odin’s knowledge. Tolkien’s One Ring was also extraordinarily powerful, and was forged by the greatest of the Elven smiths, Celebrimbor.
Tolkien didn’t skimp on the Catholic themes, either; in fact, many of the aforementioned Norse-inspired beings also had Christian aspects. The Ainur, or the Valar as their physical forms were called, were angelic beings who oversaw Middle-earth under Iluvatar, the omnipotent creator deity. Istari were a kind of Maiar (a lesser Valar) who were sent to Middle-Earth by Iluvatar and the Valar to quietly stir up rebellion against Sauron and his works. Gandalf and Saruman were a part of the Istari. They were, like angels, sent to inspire people to do worthy things and rebel against the power of evil.
Countering these angelic figures are two parallels for Satan: Melkor and Sauron. Melkor was prideful and fell out of favor with Iluvatar and out of grace, becoming the first Dark Lord, Morgoth. Sauron, once one of the Maiar, was Morgoth’s chief lieutenant. Long before the creation of the Rings of Power, Sauron was attempting to influence the peoples of Middle-Earth down evil paths. Sauron tempted the ancient Numenoreans, the ancestors of the Men of Middle-Earth, to their destruction. The isle of Numenor, in fact, was similar to Eden: it was a perfect place to live until Sauron came and tempted its people to rebel against the Valar. Their rebellion resulted in their expulsion from Numenor and their banishment to Middle-Earth.
The parallels to the devil extend into the actual Lord of the Rings story—according to the appendices to Return of the King, the day Frodo destroyed the One Ring was March 25th, a day traditionally associated with Good Friday and the ultimate triumph of good over evil.
It would be the work of a thesis or at least a very long research paper to get into all the religious themes and inspirations in Tolkien’s work, but if you think I’ve missed something important, let me know in the comments!