One of the reasons that the Lord of the Rings trilogy is so beloved as a book-to-movie adaptation is because of how the films managed to include so many characters and details from the story in a way that didn't overstuff the movies or make the three-plus hour runtimes feel like three hours. Despite how expansive Tolkien's original books are, the films managed to include most of the important scenes and characters, and only cut out the bare minimum. That being said, there are still a few characters who only appear in the books and never get the chance to shine in the movies.
Again, for the most part, they were cut out for a good reason, and it might be overwhelming for the general public to have to deal with as many minor characters as Tolkien originally included. One that is often pointed to as an example of this is Tom Bombadil, but there's another character who is quite important to the world of Middle-Earth that is replaced with someone else in the films. This missing character is the Elf Glorfindel, who was a source of assistance to Frodo on his quest. However, his role in Middle-Earth as a whole is much greater, and despite being minor enough to cut from the films, he may have been one of the most powerful Elves in Middle-Earth's history.
Glorfindel in The First Age
Glorfindel was born in Valinor during the Years of the Trees, which is the name for the period of time between the founding of Valinor and its Darkening, when it was lit by the light of the Two Trees while the rest of Middle-Earth was still in the Great Darkness. During the First Age, he was appointed the Lord of the House of the Golden Flower, which was one of the noble houses of the Elven realm of Gondolin. Glorfindel was a captain of the king and greatly beloved by the Gondolindrim.
In the year F.A. 510, Morgoth (the being that represented the ultimate evil in Middle-Earth) attacked Gondolin. Glorfindel was able to make it out with another group of survivors of the Fall of Gondolin, until they were attacked by a group of Orcs led by a Balrog at the pass of Cirith Thoronath. Glorfindel fought the Balrog and managed to slay it, but the creature grabbed him by the hair at the last second and sent them both tumbling into the abyss together. Thoronath, the Lord of Eagles, retrieved Glorfindel's body and returned it to his people, who buried him on the mountains that surrounded Gondolin.
The Second Age
As the Second Age began, Glorfindel’s spirit had traveled to the Halls of Waiting, where he lingered with other souls who had fought against Morgoth. Because of his heroic sacrifice and the good deeds he had done while he was alive, Manwë granted him re-embodiment and sent him to live on Middle-Earth. This may sound familiar to Lord of the Rings fans; it turns out that Gandalf wasn’t the only being to die fighting against a Balrog only to be reincarnated stronger than ever before. At this point, Glorfindel was considered an equal to the Eldar and Maiar, and his powers are described in an angelic fashion.
Glorfindel was sent to Middle-Earth around the time that the Blue Wizards were, just after the forging of the One Ring in the Second Age, and his task was to assist Gil-galad and Elrond in the fight against Sauron. In the Battle of Fornost, Glorfindel’s battle against the Witch-king of Angmar was victorious in that it caused the Witch-king to retreat. It was then that Glorfindel predicted that no mortal man would ever be able to defeat the Witch-king. This, of course, comes up again during Eowyn’s battle with the Witch-king at the Battle of Pelennor Fields, where she is the one to finally slay him.
The Third Age and The War For The Ring
During the War, Elrond sent a group of Elves to search for the Ring-bearer (at this time, Frodo Baggins) and Glorfindel was one of the Elves with this task, mostly because he did not fear the Ringwraiths and had a presence in both the Seen and Unseen worlds. When he did encounter the Nazgûl on his mission, they fled at the sight of him, and Glorfindel was able to find Frodo with Aragorn and helped lead them on to Rivendell. When the Nazgûl tried to approach them again, Glorfindel sent a gravely wounded Frodo ahead on his horse, who outran the Black Riders until they reached the Ford of Bruinen, the great river that protected Rivendell and was under the control of Elrond.
Frodo turned back to try and fight the Nine Riders, despite his weakened state. Glorfindel showed his power to the Ringwraiths and drove them into the river, where they were swept away by the enchanted waters that protected Rivendell. He then led the company the rest of the way to safety. This part of Glorfindel's story is portrayed in the films, but it is given to another character. Arwen takes on the role of Frodo's protector in this early part of The Fellowship of the Ring in order to give her character a more active role and more screen time, which is a choice that works well for the movie adaptation. Introducing a new character like Glorfindel who wouldn't be seen for the rest of the story would only be confusing for the audience.
In the books, Glorfindel was also at the Council of Elrond, and made the suggestion that the Ring should either be given to Tom Bombadil or cast into the sea to keep it away from Sauron, but Gandalf didn't believe this would be sufficient enough, as the Ring could still resurface after hundreds or thousands of years. Glorfindel was also briefly considered to be a member of the Fellowship, but it was decided that his powers wouldn't be of much use against Mordor in a mission that required so much secrecy. During the rest of the War, Glorfindel is never mentioned. After the Ring is destroyed, he travels with Elrond's company to the wedding of Aragorn and Arwen, and he is once again never mentioned after that. It's fair to assume that he eventually sailed to Valinor with the rest of the Elves, now that the age of Elves was over.
Glorfindel is an interesting character because he was given such immense power, but doesn't come into play as much in the main story of Lord of the Rings as one might think. His character is another example of Tolkien's immense worldbuilding, and that even someone with an interesting past who was reincarnated and was one of the most powerful Elves could be a minor character in the world at large. If anything, it drives home the message of Lord of the Rings that a person (or a Hobbit) doesn't necessarily need to be big and powerful to leave a great impact on the world.
