One of LoTR's Most Powerful Elves Was Created By Tolkien's Mistake
Yes, despite being extremely meticulous with his canon, Tolkien made real – or alleged – mistakes here and there. The one we're about to tell you, however, is probably real. But what mistake, you might ask?
Well, the one familiar to Tolkien lore buffs. There are two powerful elven warriors named Glorfindel in the history of Middle-earth. The first one lived during the First Age and became legendary for being the only Elf on record to definitely kill a Balrog in personal combat during the fall of the elven kingdom of Gondolin, even if he perished in that battle as well.
Meanwhile the second one lived several thousands of years later, and was cut from Peter Jackson's film adaptation of The Lord of the Rings in favor of giving more scenes to Arwen. In the book, it was he who played the crucial role in saving Frodo from the Nazgûl pursuit.
Where's the mistake, though? It's not like the two different characters separated by a vast gulf of time cannot have the same name.
But as a matter of fact, they can't.
One of the world-building rules Tolkien set for himself was never reusing elven names. Which is understandable, given that his elves are naturally immortal.
Even if they perish by violence or accident, their souls still persist in the world. So it is reasonable for a race like this to never reuse personal names. Furthermore, Glorfindel who appeared in The Lord of the Rings was specifically noted to be a firstborn elf, as old as the whole elven race, and so he had to have been alive at the same time as Glorfindel of Gondolin.
And when Tolkien noticed this snarl, he decided to just work it into the story. Moreover, he did not have to work too hard on an explanation. When the first Glorfindel died, his spirit went to the Halls of Mandos, as normal for elves, then eventually was granted a new body and allowed to reenter Valinor, which did not happen to every elf, but was not exactly an exceptional fate.
Then, when the Valinor army went on to bring down Morgoth at the end of the First Age, he simply joined them, and remained in Middle-earth, after the war was over.
Consequently, by the time of The Lord of the Rings, Glorfindel had the most distinguished record of any elven warrior in Middle-earth, and power which made him tower over even the unkillable Nazgûl.