This is Fanon for Tolkien's Legendarium, mostly for The Lord of the Rings, but also for other works such as The Silmarillion.
Canon for this fandom is notoriously shifty — what with J. R. R. Tolkien constantly revising his ideas — and the films can't help either. The best that we can do is check what Tolkien wrote.
- The Russian Tolkien fandom has a set of very specific Fanon, mostly First Age-related, most of which was established by published big fanfics. (Yes, there is a bootleg Expanded Universe version of Arda in Russia, illegal in most of the world but legal in Motherland itself.)
- The (common to most Tolkien fandoms) notion of Celegorm the blond (stemming from the texts where he is called "the fair" in contrast to Caranthir "the dark".)
- The notion that the Feanorians and their warriors wore a uniform of red, black and silver
- The notion that there were human black knights in Angband (popularized by The Black Book Of Arda)
- The names and personalities of Finrod's ten faithful elves (from Beyond the Dawn) and of the Nazgul (from The Great Game, and no, they are different from the ICE version known to the West)
- The existence of another Elven nation, which followed Melkor but are neither Orcs nor evil, called Elleri Ahe (again The Black Book Of Arda; their treatment by non-fans of that varies).
- The term "Primordial Age" (Prednachalnaya Epokha), not appearing in any of Tolkien's writings, used to mean the Years of the Lamps and the Trees, as opposed to the Years of the Sun (the "proper" First Age).
- The numbering of the houses of the Noldor in the same style as the houses of the Edain are numbered: the Feanorians are the First House, the Fingolfinians are the Second House, the Finarfinians are the Third House.
- Fans have ideas about female characters, especially daughters of Men, but also Elves and Hobbits. A woman always wears a dress, never breeches or trousers. If a woman is on a horse, she always rides sidesaddle, never astride. Some fans enforce this even when the woman must hike or ride for long distances.
- Fans often add the title "Lord" or "Lady" to characters. Fan fiction has "Lord Erestor" and "Lord Haldir". In canon, a lord or lady is almost always the first man or woman of some place or people, like Elrond "Lord of Rivendell" (LotR Book II, Chapter 1), Denethor "Lord of Gondor" (V, 1), and Éowyn "lady of Rohan" (III, 6). An exception is Gandalf as "Lord Mithrandir" (V, 1). Some fan characters have "Lord" or "Lady" as a rank without anywhere to lord over. Lord Kinsey in Home with the Fairies lives in Minas Tirith, and might be lord of nothing but his own household. In some fan stories, "lady" is no longer a title, but a polite label for any random woman, like lady Helanthir in Troubled Waters.
- Fans do not agree on whether things that appear in the earlier drafts of The Silmarillion (and its predecessor The Book of Lost Tales) are canon if they are not contradicted by the later, published, version. For instance there is a part in The Book of Lost Tales which describes how when Arda was first created, a number of creatures from outside the world fled into it; hence not everything in the world is something which the Valar put there (the most prominent example being the Faerie). This is of interest to fans because it provides a possible origin for Ungoliant and Tom Bombadil, but the fact that the passage doesn't appear in The Silmarillion casts doubt on this.
- It is often believed by Silmarillion fans that the eponymous Silmarils are Artifacts of Attraction similar to the later One Ring. There is no real evidence for this, and the text casts some doubt on it.
- Fans often prefer the Noldor genealogy from Tolkien's drafts (where Orodreth was a son of Aegnor and Gil-Galad a son of Orodreth) to the one in the published Silm (where Orodreth is a brother to Aegnor, Finrod and Galadriel, and Gil-Galad is a son of Fingon). The hard canon genealogy makes more sense because of Gil-Galad's title as the High King of the Noldor, which would be impossible for him as a son of Orodreth.
- dwarfling and elfling — These words only appear in fan fiction. The suffix -ling is for "little", so an elfling is a little elf, an elf-child. Tolkien never used "dwarfling" nor "elfling", though he did use some other -ling words. So in LoTR Appendix A, a young-adult dwarf is a "stripling", and an Orc addresses a dwarf as a "beardling". Also, a hobbit is a "Halfling" (LoTR II 2), and little Ents are "Entings" (LoTR III 4). (Among fans, Elfling is also the name of a mailing list about Tolkien's languages, or elf linguistics.)
- general — This army rank is fanon. Modern militaries have generals, so fans suppose that armies in Middle-earth also have them. Tolkien's armies have few ranks: Gondor and Rohan have captains, and Rohan also has marshals. The word "general" appears in LoTR IV 4, when Captain Faramir describes Boromir as "our Captain-General", which is a way to say that Boromir outranks Faramir. Boromir is a captain, not a general.
- It is noteworthy that the General rank as we know it actually descended from "Captain-General", meaning the most high ranking of captains. And the various other general ranks descended from that (Lieutenant General is one step lower than Captain-General; the Major General was originally Sergeant Major General, which is one step lower than Lieutenant).
- The aforementioned Russian fanon (specifically, Beyond the Dawn) has a whole set of military ranks used in Morgoth's army.
- human — Tolkien's characters never use the word "human". Fans use "human" for the race of Men; but a few fans also use "human" for Dwarves, Elves, and Hobbits, because those races also have human traits.
- Rohirric — This adjective for Rohan is a fan invention. Wikipedia's article for Rohirric traces this word to Robert Foster, author of The Complete Guide to Middle-earth. The word Rohirric puts the English suffix -ic on the Sindarin word Rohirrim.
- Minas Tirith, the city of seven circles, is where the wealthy live closer to the castle, while the lower and outer levels attract poorer and rougher folk. This is how The Games of the Gods and A Far Green Country depicted the city. This is only a guess, but perhaps a good guess.
- The idea was actually started in Bored of the Rings back in 1960s. In that book it was played for laughs as the residents of each higher circle behaved like insufferable snobs to the guys one circle lower.
- How short are dwarves? All measurements are fanon. Some fans think that dwarves are taller than 5 feet (152 cm). In the fan story Worlds Apart, Nymeria is 4 feet 11 inches, and the dwarves are taller than her. This might be too tall, because in canon, the secret door to Erebor is 'five feet high and three broad' (The Hobbit chapter 11), so dwarves are probably under five feet.
- Fans assume that Thorin, Fili and Kili are, among the thirteen dwarves of The Hobbit, the only dwarves in Durin's line. They assume wrong. LoTR Appendix A reveals that Balin, Dwalin, Óin, Glóin, Ori, Nori and Dori are in Durin's line. Bifur, Bofur and Bombur are not.
- Dwarf-women have no beards. This is probably wrong: LoTR Appendix A states of dwarf-women that "They are in voice and appearance, and in garb if they must go on a journey, so like to the dwarf-men that the eyes and ears of other peoples cannot tell them apart". Therefore, Dwarf-women have beards like Dwarf-men.
- Some fans believe that Elves are vegetarian, with almost no evidence. The Hobbit, chapter 8, where the Elves of Mirkwood have "roast meats", is one of several canon references to suggest that Elves do eat meat.
In The Silmarillion Chapter 17, the Elves of Ossiriand say of Men: "And these folk are hewers of the trees and hunters of beasts; therefore we are their unfriends, and if they will not depart then we shall inflict them in all ways that we can." This line suggests that Elves are not "hunters of beasts" and never eat meat, but there are other interpretations. Perhaps Elves eat meat but Men would kill too many beasts. Perhaps Elves eat fish, not beasts of land. Perhaps the Elves of Ossiriand are vegetarians but other Elves are not.
More recently, the movie of The Hobbit: An Unexpected Journey (2012) has a scene where the Elves of Rivendell serve vegetarian food to the Dwarves. But this is not in the book.
- Fans are not sure how many elves have golden hair. LoTR Appendix F says of the elves, 'their locks were dark, save in the golden house of Finarfin' (or in older editions, 'house of Finrod'), but that isn't all true, because in The Silmarillion, Finarfin is the son of Indis of the Vanyar, and the Vanyar have golden hair. Conflating elements from the books and movies, a common assumption after the movies was that, in Middle Earth, the remaining Elves have golden hair and the half-Elven have dark hair as this is how they are depicted on screen—the half-Elves of Rivendell shown with dark hair and the Elves of Lórien and Mirkwood are shown with golden hair. The movies do not distinguish between the half-Elven and the Elves at all; they are all referred to as Elves.
- Orcs in fan fiction like to ravish the daughters of Elves and Men. The canon is too vague; we know that orcs did something terrible to Celebrían, but not exactly what; it may have been rape, it may have been torture, it may have been something else. Fans suppose that they raped her. Even if orcs prefer to rape other orcs, there might be at least a few orcs who rape other races.
- Aragorn was orphaned at two. This is downright contradicted by the Appendices to LoTR: Aragorn's father died when he was two, but his mother lived until he was in his seventies.
- It's also very, very commonly accepted that Aragorn and Legolas knew each other well before The Fellowship of the Ring takes place. It's everything but canon now. It does make sense when you consider the facts though: Elrond and Thranduil probably keep some form of regular contact, and so given that he's Thranduil's son this would mean Legolas has probably spent a decent amount of time in Rivendell or at least visited it, where Aragorn has lived most of his life up to the Fellowship.
- Bolg, the orc leader in the Battle of Five Armies, is sometimes imagined as seeking revenge for the death of his father Azog. He was killed 142 years prior by Daín Ironfoot in the War of the Dwarves and Orcs. There is no canonical mention of Bolg's motivations, or how he related to his family.
- Elrond was the romantic partner of Gil-galad, the last High King. Canon has no gay romance, but leaves enough room for one. Their romance would explain why Gil-galad gave the ring Vilya to Elrond, and why Gil-galad had no children to become High King after him. Also, Gil-galad died at the end of the Second Age, and Elrond did not marry Celebrían until the Third Age. This isn't enough to prove that their love was romantic instead of just platonic.
- Erestor is the grim headmaster type in Rivendell. That's not in the books. He is only "Lord Erestor" in fan fiction. Erestor in canon is "the chief" among "counsellors of Elrond's household" (LotR Book II, Chapter 2). Fans also ship Erestor with Glorfindel.
- Figwit or Melpomaen is not in the books. His names are Fan Nicknames for a background character in Peter Jackson's movies of The Lord of the Rings.
- Fili and Kili are caught in a Continuity Snarl about who is older. In The Hobbit chapter 8, Thorin says, 'Fili is the youngest' when Kili is also present, so Kili is the older brother. Then in LoTR Appendix A, the family tree shows Fíli born 2859 and Kíli born 2864, so Fili is the older one. Most fans accept that Fili is older, because most references copy the years from LoTR, and because Peter Jackson's movies present Kili as the younger brother. Fans have also exaggerated the age difference, so Kili has less experience and maturity than Fili; but The Hobbit happens with 2941 (in the timeline from LoTR Appendix B), so their ages are close, about 82 years for Fili and 77 for Kili.
- The idea that Glorfindel of The Silmarillion is the same elf as Glorfindel of The Lord of the Rings comes from Tolkien himself, so it might be canon! Tolkien wrote in an essay (found in The Peoples Of Middle Earth) that after Glorfindel died in The Silmarillion, he came Back from the Dead before The Lord of the Rings. To reduce Continuity Snarls, some fans omit essays like that one from continuity. This allows that the two Glorfindels are two different elves.
- If the two Glorfindels are the same, fanon decides who knows so. In Ancient Languages and I Am NOT a Mary Sue, everyone in Rivendell knows that the two are the same, but in The Games of the Gods, this is more of a secret.
- Glorfindel of Rivendell is "Lord Glorfindel" in fan fiction. Gandalf says of Glorfindel, "He is an Elf-lord of a house of princes" (LoTR II 1), so "Lord Glorfindel" is probably correct.
- Many fans think that Legolas is the eldest son of Thranduil and the next king. Legolas is an only child or has a younger sister. Canon never mentions any children of Thranduil other than Legolas, but they might still exist. A few fan stories suppose that Legolas has an older brother, which is not against canon.
- The mother of Legolas (and wife of Thranduil) died before The Lord of the Rings. This idea is common, though each fan story gives a different version of her death. Fans kill the mother because they want Legolas to have more angst. The Games of the Gods, Book One, Chapter 75, defies this idea by declaring, "yep, she was still alive".
- What hair color has Legolas? Peter Jackson's adaptation of The Lord of the Rings might have settled the fan arguments. He's blond. The books make only vague references to his hair color. In The Hobbit, the Elvenking has gold hair. This king is Thranduil, father of Legolas; so it is plausible that Legolas inherited gold hair. The Lord of the Rings puts that most elves have dark hair, but is vague about Legolas. Some fans still believe that movie Legolas and book Legolas have different hair colors; the authors of The Games of the Gods, I Am NOT a Mary Sue and What Grace Has Given Me defy the movie and write that Legolas has dark hair.
- He is very often known in fanfics as "Legolas Greenleaf." Fans who do their research know that "Legolas" actually means "Greenleaf," which means that those fans are calling him "Greenleaf Greenleaf." Legolas Thranduilionnote is one often-used alternative. Mind, the fact is that elves don't seem to have last names at all, given that none is ever mentioned in canon.
- OTOH Galadriel's message to him via Gandalf starts "Legolas Greenleaf long under tree", so at least one use is canon.
- Lothíriel of Dol Amroth is almost always said to be a trained healer, even though this never appears in any source material. She also invariably has dark hair (unsurprising given that she is Gondorian), and her canonical relationship with Éomer is frequently portrayed either as a Suddenly Suitable Suitor scenario or as a Perfectly Arranged Marriage.
- Morgoth, in many fan portrayals, simply looks like a bigger version of Sauron's physical form the Peter Jackson films. That's because Jackson used illustrator John Howe's Morgoth for movie Sauron. Howe was also hired for movie concept art.
- Melkor (and sometimes Morgoth) is depicted as a Byronic-looking, very tall, heavily muscled man with long black hair, who always wears gloves to hide his burned hands and walks with a limp because of the wound sustained in the duel with Fingolfin. The latter two traits are particularly common in the Russian fandom, where he has one more characteristic trait: his hair turns from black to white post Mandos. In other versions, he shapeshifts between the Byronic man and Howe's giant armored monster at will, like in Beyond the Dawn.
- Mairon is given next to no physical description in the books, other than he was tall, 'fair', and had intense eyes. He is commonly depicted as a red-head (due to his fire motif), or as a reddish/golden blond (to match the one ring).
- Radagast is a character in Peter Jackson's The Hobbit movies, but only appears in flashback in The Lord of the Rings. He's barely even mentioned in The Hobbit, mentioned once by Gandalf as a "good cousin". He was shown to be a friend of beasts and is referred to by Saruman as a "bird-tamer", but mostly, fans take his character traits from Peter Jackson's films.
- The two blue wizards, Alatar and Pallandro, are just barely canon. There are mentions in The Lord of the Rings of there being five wizards, all told, but you'd have to look into the posthumous history of Middle-earth books, as well as Tolkien's letters, to learn their names, or anything about them. Even then, we don't learn much, and they even have alternate names, also supplied by Tolkien, Morinehtar and Rómestámo. However, as Saruman is known as Curunìr in Sindarin and Curumo in Quenya, and Gandalf is Olórin in Quenya and Mithrandir in Sindarin (also Tharkun, but we don't know by whom), these alternate names could just be translations. There have been reams of fan fiction about Alatar and Pallando, including images of them, and attributes such as being masters of the waters or the seas. Other fics stick to the semi-canon idea that Alatar was more affiliated with forests and Pallando was a scryer, or "Far-Seer".
- Tauriel is not in the books. She comes from Peter Jackson's films of The Hobbit.
- Thranduil is apparently an alcoholic who regularly beats Legolas senseless. This is highly unlikely, based on what we know of elves in general and Legolas in particular.
- Merry has no children on the family tree in the appendices, though it is mentioned that he passed the title (and job of) Master of Buckland over to his son when he and Pippin left for Minas Tirith in their old age. Tolkien himself said his children were not on the family tree due to lack of room but that he did have offspring. Fans are left speculating as to how many children he had but most fanfic writers who touch upon the subject agree that he had a daughter named Éowyn and many speculate that his oldest son was named for Théoden (similar to how Pippin named his son Faramir).