The opening shot of every episode (the shot which contains the episode's number and title) is accompanied by a melody. The melody for any given episode is unique and never repeated exactly in any other opening shot. Often, this melody characterizes the episode's most significant event. For example, the melody in "The Painted Lady" is part of the Painted Lady's theme, and in "The Firebending Masters," it is a slow version of the Sun Warriors chanting. The melodies of the first and the last episodes of the series are the different versions of the Avatar theme.
Zuko was one of the last characters to be written into the show. The Fire Lord was meant to be the show's main antagonist, but the writers realized he would not be able to cause Aang and his friends trouble sitting from his throne. Zuko was then written into the show.
Mako, who played Uncle Iroh, passed away in the middle of recording his parts for the last seven episodes of season 2. They had to quickly re-cast the part of Iroh. The re-casting put a halt to production on season 3. Mako's part was succeeded by Greg Baldwin in the third season.
Only five of the characters throughout the series have their age explicitly mentioned: Aang is 112 (though only 12 biologically), Zuko and Yue are 16, Toph is 12, and Tom-Tom (Mai's brother) is 2. It is also mentioned that Mai is fifteen years older than her brother, which makes her 17. Besides Aang, at least two other characters are over 100 years old: Bumi (who knew Aang before he got frozen) and Guru Pathik (who knew Monk Gyatso). Certain pieces of information from various episodes also imply that Firelord Sozin, Avatar Kyoshi, and Avatar Kuruk had lived for over 100 years each.
During the opening credits, five silhouetted figures are shown demonstrating various bending styles. Four are identifiable as characters from the show: the Waterbender is Master Pakku of the northern water tribe; the Earthbender is Sud, Roku's earthbending teacher (he was also an early prototype character design for Toph, but that plan was scrapped); the Firebender is Princess Azula; and the Avatar who demonstrates all four bending arts is Roku, the Avatar before Aang. Although all four were present in the opening credits since the first episode, they actually make their first appearances in episodes 18, 46, 12, and 7, respectively (although a statue of Roku is shown in episode 3 as well). The Airbender is Aang.
The calligraphy on the top and bottom of the map form a rhyming couplet when read aloud in Chinese. The characters at the top read "Powers are divided into four," while those at the bottom read "The world is guided by one."
The symbols of the four nations that are written in the map of the avatar world has a literal meaning in Chinese calligraphy. For example, the symbol of water is joined with another that means virtue; for the one of earth, it means strong; for fire, it means fierce, and finally for of air, it means peaceful.
The character of Admiral Zhao was inspired by the character William Tavington from The Patriot (2000). Casting director Maryanne Dacey was asked to find someone like the character and managed to get Jason Isaacs, who portrayed Tavington in the film.
Katara's name was originally Kya in the unaired pilot episode, but was changed before the start of the series proper. However, Kya was used for the name of Katara's and Sokka's mother later in the series.
Counting the episodes where they do not have any lines, the most prominent characters of the show are Aang, Katara, and Sokka, who appear in every episode of the series except episode 27, "Zuko Alone" (although Aang's spiritless body can be seen during the "Previously, on Avatar..." introduction). The second place belongs to Momo, who appears in 56 episodes, followed by Appa with 54, Zuko with 48, Iroh with 39, and Toph with 36 episodes. The most frequent recurring character is Azula, who appears in 22 episodes.
In the first episode of each season, Aang is waking up. In episode 1 of season 1, he awakes from an iceberg; in episode 1 of season 2, he awakes from a nightmare, and in episode 1 of season 3, he is awaken from being knocked out by Azula in the previous season.
The name of the princess from the Northern Water Tribe (and Sokka's first girlfriend), Yue, can be (depending on the tones) the Chinese word for "moon." Suki, the name of Sokka's second girlfriend (more commonly anglicized as tsuki), also means moon, but only in Japanese.
The firebenders' duel, which plays an important role throughout the series, is called "Agni-kai." "Agni" is a Sanskrit word for "fire," and is a name of a Hindu fire deity. "Kai" can be translated from Japanese as "meeting" or "together." "Fiery meeting" is an adequate description of the Agni-kai.
Although it is never explained just how Sozin's comet gives Fire benders enhanced strength, within the theology of the show, it is possible (if not likely) that as the comet skims the atmosphere, it acts like a "second sun," giving them a temporary extra boost in power.
In "Zuko Alone," Zuko comes across a man cooking by a fire. Realizing how hungry he is, he then prepares to attack and steal the food, but decides against it once he sees the man take the food to his pregnant wife. This is the same couple that the "Avatar Gang" come across in "The Serpent's Pass."
The fate of Zuko and Azula's mother, Ursa, is never revealed in the series. One of the last scenes in the entire series features Zuko visiting his father in prison, asking what happened to their mother. The creators originally intended to make a television movie special about this quest, making the near series ending scene have sense to it. However, the idea was scrapped in favor of The Legend of Korra (2012-2014). The story was instead revealed in "The Search" comic books.
"Lake Laogai," the headquarters of the Dai Li agents, has a meaning in Chinese; Laogai is short for Laodonggaizao, which means "reform through labor" and is the name of the Chinese political prison camps where many political opponents were incarcerated during the 1960s, and is still in existence.
Many have wondered if this series is considered to be anime. United States fans stated that since it is not animated in Japan, it is not an anime series. However, many fans from Japan say that anime is not based on nationality, but rather in animation style. Because of this, the Complete Series box-set has been reported to be found with other anime box-sets in video stores.