Warning: Long fanrant below.
I've probably been in the TLK fandom much longer than what could be considered normal. I first discovered it around the time "The Lion King 2: Simba's Pride" came out, and quickly became immersed in the vast world of TLK fan art and fan fiction. I became familiar with The Chronicles of the Pride Lands and its story of Mufasa and Scar's upbringing, and I took such a liking to Tanabi that I created my own version of him and wrote several stories and numerous pictures featuring him. (This was mostly due to my disappointment with Kiara and "Simba's Pride" in general.)
Though fan contributions to lionking.org weren't always that on-topic in its early days, they weren't all that off-topic either. There were many fan-created characters who tied into the movie universe in some way and they were featured in many stories and pictures by multiple authors and artists. These included Scar's son Kisasian, the leonine gods Mano and Minshasa, and of course, Simba's son Tanabi.
For a long time, things remained more or less the same on the archive. Then slowly, a new aspect of the fandom emerged and began to grow:
In this context, "semi-canon" refers to material based on the movies, but not actually part of them. The prime examples of semi-canon in the TLK universe are The Lion King: Six New Adventures, The Brightest Star, and the numerous comics published in countries outside the United States. TLK6NA introduces Simba's son Kopa and several other new characters, The Brightest Star tells about Simba's great-grandfather Mohatu, and the comics introduce us to a plethora of new characters, both lion and non-lion. For people unfamiliar with the TLK fandom, it's pretty deep rabbit hole to venture down.
Once scans of these various works were made readily available, the characters from them quickly gained popularity, and once the initial excitement had calmed down, numerous theories about them began to spring up. A couple of the most popular theories are that Kopa was killed by Zira and that Uru is Mohatu's daughter. Recently, there have also been many attempts to squeeze as many semi-canon characters as possible into various TLK family trees in an attempt to fill in various gaps (such as who Nala's father is, who Nuka, Vitani and Kovu's fathers are, etc.).
However, many of these semi-canon works contradict the movies, each other and even themselves at times. For instance, the book Friends in Need tells the story about how Mufasa met Zazu as a young lion and allowed Zazu do become his advisor after he helps Mufasa save Sarabi. This contradicts the TLK6NA story "A Tale of Two Brothers", which says that Zazu became Mufasa's advisor after Mufasa became king since Zazu's mother Zuzu was such an excellent advisor to Mufasa's father. Nala's eyes are also described as being "amber" and "golden" in TLK6NA, and of course, the most infamous contradiction in that series is Ahadi's mane and eye color (he is described as having "a long black mane and green eyes" in the text, yet has a brown mane and red eyes in the illustrations). There are also many small and large contradictions in the comics (a small one would be cub Simba claiming that he can't sing in "An Unusual Choir", while a large one is cub Simba, Timon and Scar all appearing in the same place and time in "Roar").
Any way you look at it, you have to pick which elements from semi-canon material you accept and which ones you reject. There are two official explanations for how Timon and Pumbaa met, one in the Timon and Pumbaa TV series and one in TLk1.5. However, despite the excessively cartoony atmosphere and extremely anthropomorphized characters in the T&P episode, little if anything contradicts TLK, while TLK1.5 contradicts TLK repeatedly (Timon meeting Rafiki prior to the events of TLK despite not recognizing him in TLK, Timon and Pumbaa trapping the hyenas during the battle at Pride Rock when the hyenas should have been on top of Pride Rock overhearing Scar betraying them, "I Just Can't Wait to be King" apparently happening the day after Simba's birth, to name a few). There are even a few people who refuse to accept SP as part of the TLK universe because of its various flaws (such as the gaping plotholes, the ways that the recurring characters are portrayed, the new characters' general lack of appeal, "Upendi", etc.).
Over the years, mountains of semi-canon material have formed, and the theories surrounding the various characters are even more numerous. Though I certainly have had a lot of fun drawing the various semi-canon characters over the years, I've recently started thinking back to the old days -- the days where the most common name of Simba's son was Tanabi, not Kopa; the days when Ahadi's mate was named Akase much more often than Uru.
Back in 2000, I wrote a story about Tanabi being kidnapped as an infant and returning after TLK2 in my version of TLK3. Not many people had heard of Kopa back then, and Chaka was equally obscure. This character was just my version of Simba's son, whose design I based off of the cub at the end of TLK. I knew Tanabi wasn't "canon", and it didn't matter to me that he wasn't. What mattered was drawing him and writing stories about him. Then, some time before The Lion King 1.5 came out, I got an email from someone saying that "It is about timon and pumba's side of the story" and that I should "stop making up this character who you believe is another cub at the end of the first movie" and "stop making bull stories about the third movie. It is not about Simba's long lost son (which he doesn't have)".
This email puzzled me. My story was one of many stories at the time called "The Lion King 3", and I'm sure none of those stories were written about the third movie, especially since the majority of them (my own included) were written long before TLK3 even went into production. And even if TLK2 makes it fairly clear that Simba doesn't have a son, what's wrong with making one up? Isn't making things up one of the main facets of fan material?
Sometime after I wrote my version of TLK3, I read a fanfic called "Tales from the Outlands Volume I - The Tale of Zira". In that story, Nuka is the son of Scar and a female hyena, and the father of Vitani and Kovu is a lion named Kisasi, who had gray fur, a fire-engine-red mane and scars over both of his eyes. Even back when I first read that story, I knew that it was biologically impossible for a lion and a hyena to reproduce, strongly felt that Zira was Nuka's real mother, and found it odd that a lion with a design so different than the rest of the TLK characters would not only appear alongside them and be the father of two cubs who look hardly anything like him.
But still, this story stuck with me for a long time, and it didn't stick with me because it followed semi-canon material like TLK6NA as closely as possible or that it always adhered to most prevalent fan theories of the time (such as the one that Nuka is the son of Scar and Zira). It stuck with me because it was a good story. It was well-written, powerful, and above all, unique. It didn't matter that the story wasn't "canon" enough. What did matter was that it was A GOOD STORY.
However, I've seen more and more people getting uptight about how "canon" TLK fan art and fan fiction is over the years. A prime example of this uptightness often appears on fan-made family trees which include original characters that are plugged into the TLK universe (as the parent, sibling or offspring of one or more canon characters), there will occasionally be one or two commenters saying something like, "Hey, [original character name] isn't [canon character name]'s father! [semi-canon character's name] is!" or "This tree is wrong! [canon character 1] and [canon character 2] never had any cubs!"
And as if the semi-canon fanatacism wasn't bad enough, some fan theories gain so much popularity that some people start proclaiming them as fact. I've seen people claim that Ahadi's fur color is described as being golden in TLK6NA, yet the color is never mentioned in the books at all. I've seen other people claim that Uru is Mohatu's daughter based on this misinformation, saying that Uru must be dark if Ahadi is golden, Mohatu is dark, ergo she must be his daughter. I actually got a comment on a picture where Ahadi was dark and Uru was golden that was yelling, "Those aren't their regular colors!" at me.
I've also people claiming that Scar is Nuka's father, even after the head scene checker of Simba's Pride confirmed that he wasn't (as related to the rest of the fandom by a fan named Capriconfox). The theory about Scar getting scarred by Ahadi has gained so much popularity that some people are claiming that that's the real explanation for the scar. I've also seen many of people misinterpreting what they've heard about TLK6NA and saying that Scar got his scar from Boma the Cape buffalo, unaware that in the actual story, Boma was stuck in a gorge when Scar got scarred and that it was an unnamed buffalo that did the deed. And if I had a nickel for every YouTube commenter I've seen screaming that it's a fact that Kopa was either killed by Zira or was thought dead and returned to the Pride Lands as an adult and married Vitani...well, let's just say I'd have a lot of nickels.
And after being witness to this sort of thing for a while, I started thinking, "What happened to the TLK fandom?" What happened to the days when fan characters were just as accepted as semi-canon characters and most fanfics taking place prior to the events of The Lion King had a plot considerably different than the stories in "A Tale of Two Brothers", The Brightest Star and Friends in Need?
The way I see it, if any fan work you do based on TLK doesn't blatantly contradict the events of the movies, it doesn't matter. After all, it was the movies that got us into the fandom, not the various tie-in books, games and comics. If you want to incorporate the semi-canon characters into the TLK universe in some way, more power to you, but don't start criticizing someone's fan character or fan theory because "it's not canon". I mean, it's called The Lion King FAN ART Archive, not The Lion King Fan-Made But Still Good Enough to be Almost Canon Art Archive.
In closing: Don't let yourself be confined by what is dictated by semi-canon sources and popular fan theories. Don't be afraid to create a different backstory for TLK. Give Simba a son other than Kopa. Give Mufasa and Taka's parents different names and designs. Give Simba a great-grandfather with a more impressive story.
And above all: Don't let semi-canon box you in.