The cinematic universe of The Lord of the Rings has taken on a life of its own outside of the original literature by Tolkien, but for those that want to experience the full scale and breadth of the world that the author created, the books are essential. The library includes not only the three novels that make up the trilogy but also The Hobbit and The Silmarillion along with a variety of other books written and edited by Christopher Tolkien.
It's not just the general lore or obscure history that can be found in the books. Even the main characters in the movies are mere shadows of their former selves in the movies when compared to the complex figures that Tolkien created for the story. Gimli, the representative of the Dwarves in The Lord Of The Rings, had a lot more going on than the films could ever reveal. There's a lot about Gimli, son of Gloin, that only the book-readers know.
6 Named Elf-Friend
This is part of the long resolution that is even more drawn-out in the books, but the fact is that Gimli saw a lot of places that no Dwarf had ever seen thanks to his close friendship with Legolas and his connection with Galadriel. In the books, Gimli and Legolas actually bonded over their disagreement over who was more beautiful, Arwen or Galadriel, with Legolas choosing the former and Gimli the latter.
The story of Gimli being gifted with three of Galadriel's strands of hair is well known, but a lesser-known fact is that her uncle Fëanor, the great smith who crafted the Silmarils, made a similar request of her. He was refused, but Gimli's ask was granted, perhaps because of the Dwarf's humility and sincere flattery. This version of the story appears in Unfinished Tales, one of Tolkien's later incomplete books that were edited by his son.
5 A Descendent Of Durin The Deathless
The Vala Aulë actually created the Dwarves before the Elves were created, and put one of his creations under a mountain to sleep until the time of their arrival. This was Durin, who came to be known as the Deathless in later ages because of his long life, and it was he that founded Khazad-dûm. Dwarves would also refer to themselves as "Durin's folk" in his honor, and Gimli is one of his descendants.
Nain II, the great-great-many-times grandson of Durin the Deathless, had two sons, and the younger one is Gimli's ancestor. Thorin was the more favored in line for the throne, being a direct descendent of Dain, but Gimli could have put forth his own claim if he wanted.
4 Lord of the Glittering Caves
Gimli was related to the royal line, and although he never chooses the kingship for himself, he did rule a kingdom that came to be known as the Glittering Caves. After the Fellowship had broken and the War of the Rings was over, he took some of his kin to the caves near Helm's Deep in a region known as Aglarond where they built a new Dwarven kingdom.
It was here that Gimli was named the Lord of the Glittering Caves, and the new Dwarf-realm established there recalled the craftsmanship of ancient times when Dwarves worked with mithril. It was here that the news gates of Minas Tirith were constructed, and they were made of mithril and steel.
3 The Only Dawrf To Sail Into The West
The rift between Elves and Dwarves goes back to the dawn of creation. The Elves were created first, in the Undying Lands to the West, and that's why their destiny is to return. The Dwarves, however, were created in secret by the Aulë in Middle Earth. This is why the Dwarves do not go to the Gray Havens or the Undying Lands.
Movie fans never saw Gimli go west with Legolas, although it seems to be common knowledge that he did go eventually. What's more obscure is that he was the only Dwarf to go, ever, in the whole history of Middle Earth. Exactly how he got permission is a matter of speculation, as Legolas didn't have the influence to get a favor like that, but it's likely Galadriel had something to do with it.
2 Revealed Some Dawrven Speech To His Companions
Tolkien himself describes the speech of the Dwarves as "a tongue of lore rather than cradle speech" in Appendix F of The Return of the King. When conversing with those outside of their own communities, Dwarves would use Common, keeping their native languages a guarded secret among themselves.
Dwarven speech doesn't appear as often in the books as Elvish does, and comes across as more exotic because the reader doesn't see it very often. So when Gimli uses his native language with his non-Dwarf companions, especially Legolas, it's intended to indicate a level of deep trust and friendship.
1 Wasn't Fooled By Saruman
In the movies, Saruman uses his manipulative speech to try and convince Gandalf, King Théoden, and their allies, to let him go. The remainder of the Fellowship is also present, including Aragorn, Legolas, and Gimli.
Sarman makes a pathetic attempt at a mind-control spell, which is more obvious in the books than in the movie, but Théoden isn't fooled. The only other character that sees through this trick is Gimli, and that might be a reference to his natural resistance to this kind of magic. When Aulë made the Dwarves, he made them in Middle Earth, and he knew they would have to face Melkor and his magic sooner or later. The Silmarillion describes that Aulë made them naturally resistant to all kinds of magic including mind control.