Avatar: The Last Airbender

Avatar: The Last Airbender, also known as Avatar: The Legend of Aang in some countries, is a popular cartoon series created by Mike DiMartino and Bryan Konietzko. A live-action movie is being planned for the summer of 2010.

In Canon
The story takes place in a world based largely on Asian culture and centers around the concept of the four elements: water, earth, fire, and air. Many citizens of the Avatar-verse have the ability to control, or "bend", these elements, but they can only bend the element of their country. Only one person is capable of bending all four, and that is the Avatar.

World
There are four countries in the Avatar-verse.

The Water Tribes, located at the north and south poles.

The Earth Kingdom, largest of the four, taking up a huge continent in the east.

The Fire Nation, a large, volcanic archipelago in the west.

The Air Nomads, who, as their name implies, traveled all over the place. They did have four temples that served as bases of sorts, however: the Northern Air Temple, Southern Air Temple, Eastern Air Temple, and Western Air Temple.

Plot
The story follows the quest of Aang, a twelve-year-old airbender who is the latest incarnation of the Avatar. At the beginning of the story, Aang has been frozen in an iceberg for a hundred years, during which time the Fire Nation decided that peace was overrated and declared war on the other three countries. They also completely wiped out the Air Nomads in an effort to kill the Avatar so he couldn't stop the war, but seeing as Aang was encased in a giant block of ice at the time, that didn't really work.

Now, freed from the iceberg by the Water Tribe siblings Sokka and Katara and suddenly finding himself a key player in the middle of a war, Aang needs to master all four elements before defeating the Fire Lord and saving the world. Preferably before the comet that'll increase the Firebenders' power by one hundred-fold arrives in the summer. And while dodging that disgraced and banished Prince Zuko of the Fire Nation, who needs to capture the Avatar if he's going to restore his honor. Not to mention finding true love...

Characters

 * Aang
 * Katara
 * Sokka
 * Appa
 * Momo
 * Toph Bei Fong
 * Suki
 * Zuko
 * Iroh
 * Azula
 * Mai
 * Ty Lee

In Fandom
Because the show was primarily aimed at preteens, there are a number of fanbrats in the Avatar fandom. Like any popular fandom, there are also plenty of fangirls. And, of course, good, sane, mature fans who actually act like human beings.

Shipping Wars
For some reason, the Avatar fandom is rife with shipping wars. These were even more intense while the show was still running, as it was still up in the air as to who would actually end up with who. Now that the series has ended, many people are still in denial or simply like their ship better than the canonical ones, as shown by the fanfiction. Avatar is probably the only fandom where badly-written uncanonical shipping is more of a problem than Mary-Sues.

Canon Ships
Kataang: Katara and Aang. They have a beautiful relationship that realistically builds into romance, but a number of fans were put off by the fact that Aang is twelve and Katara is fourteen.

Sukka: Sokka and Suki. Most fans have no real problems with this one.

Maiko: Mai and Zuko. A pair of somewhat-angsty teenagers who don't really know what to do with each other, but make do. Plenty of fans love this one, but many more downright hate it because it paired Zuko up with someone other than Katara.

Non-Canon Ships
Non-canon ships, like all AUs, can be well-written. Unfortunately, many fans of non-canon ships forgo the ideas of good writing, characterization, and building up a canon-compliant situation in favor of ignoring, bashing, or killing off certain characters so they can get their OTP together.

Zutara: Zuko and Katara. This ship has the biggest following out of all of them. Fans decided it would work because Zuko is from the Fire Nation, Katara is from the Water Tribe, and everyone knows that opposites attract. A number of Zutarians clung to the hope that the ship would become canon, despite all the hints of Kataang and Maiko. Zutara can be well-written, and often is, but unfortunately many Zutarians tend to ignore Aang to get him out of the way, and outright bash Mai.

Tokka: Toph and Sokka. This ship can almost be canonical, as Toph has a small crush on Sokka. The pairing has a sizable following, but there was nowhere near as much drama over Tokka as there was over Kataang, Maiko, and Zutara.

Taang: Toph and Aang. Again with the idea that opposites attract, as Aang is an Air Nomad and Toph is from the Earth Kingdom.

Toko: Toph and Zuko. They seemed to have more of a sibling-like relationship in the few scenes where they interacted with each other, but some fans took it a step farther.

In Badfic
Aside from badly-done shipping, other problems that plague Avatar fanfiction include:

Mary-Sues: Though not as prevalent as the shipping, there's still plenty of them.

High School AUs: Probably thanks to all the fanbrats.

Horrible Writing: Again, fanbrats. Most of whom apparently have no grasp of how their language works.