Zuko's great-grandfather is Avatar Roku — therefore, via reincarnation, Aang... sorta. Technically.
You could also technically count Aang as Ursa's grandfather and Azula's great-grandfather, as odd as it sounds.
Waterbending is the only bending skill that was not learned from an animal. Waterbenders are said to have learned from the moon; in contrast, earthbenders learned from the badger-moles, airbenders learned from the sky bison, and firebenders learned from the dragons. The entire concept is awfully similar to animal-based martial arts in Real Life, made famous by Hong Kong martial arts movies like Jackie Chan's Snake in the Eagle's Shadow or Tiger and Crane Styles (best known for being edited into Kung Pow! Enter the Fist).
As mentioned on the main page, the bending styles themselves are based on actual Chinese martial arts (waterbending is tai chi, mainstream earthbending is hung gar, firebending is northern Shaolin kung fu, airbending is baguazhang). Exceptions not covered are:
Toph's own Earthbending style, taught directly by the badger-moles, is actually based on chow gar (southern praying mantis style, to be exact).
Metalbending, based on Xing Yi Quan, which was quite appropriately developed in captivity as well.
Bloodbending, based on Qin Na Shou, which was also quite appropriately a grapple-based technique.
Redirecting lightning is the only style taken from a sword technique, the obscure tai chi sword discipline, which is appropriate given that Iroh created the technique by watching waterbenders.
Even better is that all of the above are unique martial arts styles compared to the respective culture's norms because they are all unique to a certain character or (in the case of lightning redirection and bloodbending) a very small group.
Extra points for lightning redirection being explicitly based on waterbending techniques.
You can probably catch some differences between Katara and Pakku's waterbending styles since Southern and Northern are legitimate tai chi variants.
"Katara" means "curse" (both as in "hex" and "swear") in Greek. Of course, this is just a weird coincidence, but it's too odd to not mention. One would suspect that the character was so named because a Katar is a type of Indian dagger, though.
Word of God stated Katara's name was inspired by the French word "Cataracte," which is synonymous with "Waterfall". On a side note, there is also the Greek word "Katharos," which means "pure" and "Katarassō," which means "to spill."
The earthbender was Toph's original design, which ended up inspiring later characters such as The Boulder, Sud (Roku's earthbending teacher), and the actor playing Toph in "The Ember Island Players."
Some argue that the Airbender in the opening is Monk Gyatso. Others claim it's an older Aang (a theory largely debunked by older Aang's appearance in The Legend of Korra, who looks much different), and still, others suggest it might be one of the unnamed monks from "The Storm."
Toph was originally envisioned as a boy but the writing team thought it'd be funny to make the show's resident Boisterous Bruiser a cute little girl. The original characterization they had in mind for him was largely rolled into Bolin in Korra.
Actor Existence Limbo: After Mako's death, Iroh was relegated to only two silent appearances for the first half of season 3, before Greg Baldwin was introduced as his new voice.
Adored by the Network: Inverted on the main channel, just like with most Nicktoons series. However, on the Nicktoons Network, the show was frequently shown every day, had lots of marathons, and even got its own Avatar Extras event (which would feature pop-up facts and comments written by writers of the series). Justified, since reruns on the network have brought in some of the highest viewership numbers in the network's history.
Banned in China: Nothing in the entire franchise has ever been released in China. Given that the Air Nomads are based on the people of Tibet, this is a given but there are other factors involved as well. The censorship board isn't keen on portrayals of China by Westerners, so the fact that the Earth Kingdom is their equivalent is another strike against it. Especially saying that they do touch on its modern-day status as a totalitarian police state with the Dai Li. note Although ironically, the Dai Li was actually based on the Kuomintang's 'Bureau of Investigation and Statistics' division which was a secret police force, and the Dai Li in the show are even named after Kuomintang spymaster Dai Li. This organization is most infamous for its role in the brutal suppression of the Chinese Communist Party by the nationalists. The Bureau is still active today in Taiwan. The fact that said government gets overthrown by the Japan-equivalent probably just drives the nail deeper into the coffin for the first show.
"The Avatar always gets the girl" is a quote often attributed to Avatar Roku, when Aang observes that he married the "girl who didn't even know [he was] alive." What Roku actually says is "When love is real, it finds a way. And being the Avatar doesn't hurt your chances with the ladies, either." He's gotten flak in some fandom circles for the sexist implications of the incorrect quote, even though the correct quote is a gentle joke and he's attempting to encourage Aang, who's both fretting over his crush on Katara and his decision not to give up his attachment to her in order to master the Avatar State. In other fandom circles, it's used as a joke because Korra and Kyoshi also got the girls.
"There's no war in Ba Sing Se" is almost always quoted as "There is no war in Ba Sing Se," without the contraction. The original line is "There's no war in Ba Sing Se. There is no war within the walls."
Cast Incest: Grey DeLisle has alluded to this during conventions when she jokingly entertains the idea of her and Dante Basco dating.
While this was averted in the original version as Aang was voiced by a boy, it was played straight in Russia, the Philippines, Japan, Korea, Portugal, and Taiwan.
Not used in the show itself (12-year-old Aang is voiced by Zach Tyler Eisen), but Lampshaded in the play in "The Ember Island Players", where Aang is played by a (visibly adult) woman (voiced by Rachel Dratch). This doubles as a reference to Peter Pan, where the eponymous eternal child is traditionally played by a petite woman rather than a prepubescent boy.
Played straight with Suki and Zuko, whose voice actors Jennie Kwan and Dante Basco were in their 30s.
Played straight in Chile with Aang, whose male voice actor (René Pinochet) was almost 30! Justified that he was born prematurely and his voice hadn't changed much since childhood. Dante Basco, the actor for Zuko, also had a young voice in his late 20s when he did voice work for the show.
In The Waterbending Scroll, Momo gets into a scrape with the pirate's pet Iguana Parrot. This is a possible reference to the unaired pilot episode, where Zuko had a pet hawk that attacked Momo.
In The Return to Omashu, Aang fights Azula and her gang at a construction scaffold, much like where he fought Zuko in the pilot.
Development Hell: The Netflix Live-Action Adaptation series has gone over two years between its announcement and production. It was green-lit in September 2018 and was steadily worked on for a year. Right around the planned February 2020 start of production in Hawaii, the Coronavirus Disease 2019 Pandemic stopped it in its tracks since they had planned to film extensively on location, causing their travel to be severely limited. That summer Mike and Bryan left the project because of Creative Differences. A new showrunner was hired later that year. Netflix is still sticking by a tentative Q4 2021 production but it is at the mercy of a good rollout of the COVID-19 vaccine and an accompanying loosening of travel restrictions.
Fan Community Nicknames: Due primarily to one certain "megafan"'s infamous, long-running satire comic of the Avatar fandom, fans have come to almost unanimously accept the term "Avatards". Some people feel that in referring to the term "retard", fans' use of this label is demeaning to the mentally disabled. The creator of the comics has also openly admitted to regretting the choice of the word in retrospect. It's rarely used nowadays.
The term fell out of use after The Legend of Korra was announced, at least partially because of the Unfortunate Implications - it's now rarer to find someone in the fandom who calls themselves an Avatard than someone who doesn't.
Originally, Sozin was implied to have been relatively young when he started the war and ruled for the first 70 years of it before dying, his son Azulon was said to have ruled the next 23 years before dying and passing the title to Ozai for the past 6-7 years before the present. Things got strange during the third season when it revealed that Sozin was actually Avatar Roku's age and began the war at 82. Word of God Hand Waved this by stating that Sozin ruled for 20 years after he started the war, Azulon was born the year the war started and ruled the next 75 years of the war, and Ozai, in turn, ruled for the last 5 years of the war.
On whether or not there were plans for a fourth season with head writer Aaron Ehasz stating on his Twitter account in early 2019 that he and Bryke did in fact had plans to do such (see What Could Have Been below), while co-creator Bryan Konietzko stated on his Instagram account in April 2020 that he always envisioned it to be a three-season series with a beginning, a middle and an ending. It's possible that Creative Differences were at play.
Newbie Boom: Experienced a huge fandom boost after it was added to Netflix in May 2020. It was #1 on trending for weeks on end.
No Export for You: The series, despite being heavily influenced by Eastern mythology, done in an Animesque visual style, and possessing a more anime-like Myth Arc instead of the typical episodic nature of most Western Animation, was never successfully released in Japan in the time of its airing. The first two seasons of the original series were dubbed and advertised, but never released. A proper dub for season three and legal sales in Japan wouldn't appear until nearly a decade later when the show was made available on Amazon Prime Video Japan.
Orphaned Reference: In The King of Omashu, Bumi tells Aang that Momo would be important to his journey. This was possibly meant to be a foreshadowing of a planned plot point of Momo being the reincarnation of Monk Gyatso.
Pop Culture Urban Legends: It's frequently said that Japan hated the series because the Fire Nation's imperialism rang too close to home. It's complicated why the series wasn't received much in Japan, but that's not one of the reasons. The series was canceled after Book 2 because Japan's Nickelodeon channel failed, not because of the series' popularity. Book 3 was later dubbed years later by Amazon Video.
Reclusive Artist: Zach Tyler Eisen, Aang's voice actor, is one of the only major living voice actors from the show to not attend any fan events since the end of the show. All his verified social media accounts are either closed or private. It is known that he attended Syracuse University and currently works as a photographer for the Conde Nast group (indeed, his name can be seen in the credits for several Vogue interviews) but very little is known aside from that, due to zero fan interactions. Ultimately, he finally resurfaced in a 2020 interview, where he revealed that he mainly stayed out of the spotlight because he just wanted to live a normal life, but still maintains a huge amount of respect for the show.
Screwed by the Network: This show was consistently bringing Nickelodeon some of their highest ratings in spite of the fact that its premiere slot frequently changed, had a hit-or-miss amount of advertising, and went on hiatus constantly, most infamously having a nine-month gap between seasons two and three, followed by a seven-month gap in the middle of the third season. If you missed an episode and didn't have Nicktoons Network or have the show on DVD, you were basically out of luck, since the show rarely (if ever) got reruns, as Nickelodeon considered the continuity-heavy plot as being very unsuited for reruns on the main network. Ironically, the series is still treated much better when compared to other Nicktoons that were screwed over before and since, such as it's notoriously mistreated sequel series The Legend of Korra. The show also never had its final episodes dumped to the Nicktoons channel, something happening to several fellow Nicktoons at the time.
Originally, Sokka was conceived of as being far more stern and grumpy, but Jack DeSena's improvising and riffing on his lines were so funny that they began to adjust how they wrote him.
Additionally, in the episode "The Ember Island Players", the entire show was parodied hilariously by a play. The actor parodying Sokka wasn't funny enough and so Sokka tried to fix it by substituting his own jokes with even more hilarious results.
Unisex Series, Gendered Merchandise: The toy line excluded the female characters, particularly Katara. This is often credited as one of the reasons it never caught on and was discontinued before the second season.
"Laogai" is actually a phrase referring to a system of penal labor facilities in Communist China.
The background music in Earth Kingdom dinner scenes ('The Blind Bandit' and 'City of Walls and Secrets') is an actual traditional Chinese tune called 'Mo Li Hua' or Jasmine Flower.
From the end of "Avatar Day": fried dough sticks to represent hated historical figures do exist.note You can see the Landlord bumming some off of Donut early in Kung Fu Hustle. Long story short, Evil Chancellor Qin Hui set up the Emperor's most loyal general Yue Fei as a traitor, leading to his execution before the truth was out. The fried dough sticks are always made in pairs to represent Qin and his wife.
Energybending in the Grand Finale becomes less of an Ass Pull if you're familiar with Chinese martial arts fiction, which commonly used "the removal of his martial arts" (via crippling nonfatal injury) as a Fate Worse than Death for villains. Another common trope from this genre is having your villain driven insane with his own growing abilities... which might explain Azula (or Bumi, but he was always a little odd).
In a similar vein, Metalbending. Toph is shown using two different martial arts styles for standard (Hung Gar) and her self-developed (Mantis) Earthbending; Metalbending comes from a third style, Xing Yi Quan, developed in captivity just like Toph's metalbending was.
And blood-bending is based on Qin Na Shou, an appropriately grapple-based technique.
Toph was originally conceived as a guy. When designing the show's lead Earthbender, who was originally supposed to be a teenage boy, head writer Aaron Ehasz joked that it would be funny to see a small little girl take out all those big, burly Earthbenders. Though the idea was rejected by series co-creator Bryan Konietzko, the team still decided to work around it, and several discussions and redesigns later, Toph was born (and ironically became one of Bryan's favorite characters). Variants of her original character model make a few appearances throughout the series in bit roles, most notably as a bender in the show's opening sequence (Roku's Earthbending teacher) and THE BOULDER!
Word of God says that the screechy actor who played her in the play is a flanderized version of her original character design. Aspects of her original male visual design and characterization were later incorporated into Bolin.
Incidentally, Azula was also originally conceived as a guy; her name would have simply been "Azul."
Suki, Ty Lee, and Mai didn't exist in the original series Bible.
Speaking of THE BOULDER, the creators originally wanted him to be voiced by the Rock.
In the season 2 premiere, originally Azula was going to vaporize her captain for letting it slip that Zuko and Iroh were prisoners, but realized they couldn't do that on a kid's show.
Zuko was originally going to find Ursa. See also Cliffhanger on the main page. The production staff even planned a storyboard for it and everything.
In the Avatar Extras for part one of the Season 1 finale, it's mentioned that there was an idea kicked around for a special about Iroh's failed attack on Ba Sing Se, but it never took off.
A dropped subplot revolved around Momo being the reincarnation of Aang's mentor, Monk Gyatso.
The identity of Aang's parents was going to be revealed, but this was later dropped.
There was going to be an episode that involved Aang and Sokka getting handcuffed together.
Originally, the episode "The Warriors of Kyoshi" would have more of a Bitter Sweet Ending, ending with the gang retreating from the burning village to get Zuko to chase them and prevent him from destroying it completely. The ending was revised to have Aang use the Unagi to put out the fires before escaping.
Originally, in Book Three, Azula was apparently meant to have been in an arranged marriage, and Appa, in the season finale, would have been confirmed as female. They decided not to do this, for obvious reasons.
According to the I.P. Bible, Aang and Katara were not supposed to end up together. Aang's crush on Katara was to remain one-sided until the end. Katara actually had more Ship Tease with the then male!Toph than Aang, but nobody was going to end up in a relationship. While the show was in production, Bryke decided to have Katara/Aang happen as they came to adore Aang and realized that Kataang was their "soft spot".
Episode writer Joshua Hamilton has confirmed twice that a Zuko/Katara romance was toyed with in the Avatar Extras.
The writers originally intended to have Pong living with another character named Ping for comical reasons, but they decided otherwise as it was "not funny enough to put in the episode". In the DVD commentary for "City of Walls and Secrets", the creators revealed that they had initially intended for Pong to have a much larger comical role that would stretch to the end of the season, but that he got edited out in subsequent revisions and by the end of Book 2 they had completely forgotten about him.
Behind the scenes, pacing issues necessitated changing the third season to twenty-one instead of twenty episodes, as Sozin's Comet was originally three episodes long instead of four. After realizing how rushed the finale would have been as a result, Mike DiMartino and Bryan Konietzko expanded it to four episodes.
Aaron Ehasz wrote that he, Bryan, and Mike considered a fourth season and intended for Azula to have a redemption arc, with her brother being by her side in much the same way Iroh was for him before it was scrapped because Mike and Bryan wanted to put full focus on the live-action film. He later went deeper by saying that he intended for Aang to be deeply traumatized by Energybending Ozai, requiring another Zuko field-trip to find himself, and potentially running into a reincarnated Monk Gyatso. The actual creators have denied this, however.