Bosco

Bosco is the Earth King's pet bear. He resembles the real-life northern grizzly bear and lived in the forests along the eastern coast of the Earth Kingdom.

History
Bosco was captured in the forests along the eastern coast of the Earth Kingdom. He is the only known member of his species, although the Earth King has commanded the top zoologists of Ba Sing Se University to lead a battalion of soldiers in scouring the earth to find Bosco a mate. Little is known about his habits in the wild, but Bosco seems to enjoy roaming the grounds of the Royal Palace with his master, and has developed quite a taste for cakes and pies.

Bosco was first seen in "City of Walls and Secrets", where he was the guest of honor at a birthday party the Earth King threw for him. He was shown eating large portions of food and being fascinated when Aang performs Airbending tricks.

He was seen once more in "The Earth King", where he sat by Kuei's side. He was one of the reasons Kuei decided to hear what Aang and his friends had to say about the conspiracy due to his liking of Aang.

Bosco is shown once more in "The Guru" while Kuei was welcoming the disguised trio of Azula, Mai, and Ty Lee. Apparently Mai was forced to clean all of Bosco's "waste", saying if she cleans another pile of bear poop, she'll throw up (this may have been only to trick the Dai Li agents, however). In "The Crossroads of Destiny", Bosco was separated from Kuei after Azula ordered the Dai Li to arrest Kuei. He was soon reunited with Kuei, however, when Sokka and Toph successfully rescued him from Ty Lee and Mai (who actually wanted him gone), by trapping Ty Lee's hands and feet to the ground.

In the comic book strip, "Its Only Natural", Sokka was shown trying to get Bosco to survive in the wild. After many failed attempts of climbing, fishing, roaring, and self defense, Sokka gives up. After seeing how Bosco does not know how to be a real bear, Kuei decides to travel the world as a humble man, with Bosco by his side.

After Ba Sing Se was liberated, it can be assumed that Bosco has returned to a life of luxury and that Kuei has regained his position as Earth King.

Behavior
Bosco was very ill-mannered, loud, and slobbery, and could often be seen eating. However, the Earth King apparently did not notice this, and treated him like his son. He now travels with the Earth King undercover to see the world outside the walls of Ba Sing Se. Despite being slobbery and ill-mannered, he is very sweet to other people.

Behind the scenes
When Bosco the Bear is first mentioned to Aang and his friends in "City of Walls and Secrets" they are skeptical that there is such a creature as a "just a bear?" and suggest that perhaps it is another type of creature, such as a Platypus Bear, Skunk Bear, Armadillo Bear, or Gopher Bear. This is an inside joke, as most of the animals in Avatar: The Last Airbender are either mythical or hybrids of two different animals from the real world. He, like the Earth King, is obviously very important, as one person says at a banquet, "You don't know what I had to do to get seats this near the bear!"

The people of Chin seem to know what a bear is, as one of the punishments on their Wheel of Punishment is "being eaten by a bear" with accompanying illustration. The picture, however, seems to resemble more of that of a Platypus Bear.

Trivia

 * Bosco is one of very few nonchimerical (unhybridized) animals seen in the world of Avatar. Considering how hybrid animals are more frequent in the world of Avatar, Bosco is considered strange. Other examples of unhybridized animals include Miyuki and Wood Frogs.
 * According to DVD commentary, Bosco was named after the pet dog of an Avatar animator. Coincidentally, Bosco shares a similar name to Boskov, a bear who is a character from Evil Con Carne.
 * Bosco's claws are manicured twice a month.
 * Bosco is the only animal (apart from Momo) to ride on Appa's back.
 * A comic entitled "It's Only Natural" was released by Nickeledeon, telling the story of Sokka as he tries to reintroduce Bosco to the wild. This comic reveals several of Bosco's skills, such as his ability to use a fishing rod and to whistle.