Bosco

Bosko the bear was the Earth King's pet. He resembles today's northern grizzly bear.

Behavior
Bosko 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.

Behind the scenes
When Bosko the bear is first mentioned to Aang and his friends, they are skeptical that there is such a creature as a "bear." This maybe an inside joke, as most of the animals in Avatar: The Last Airbender are either mythical or very exotic.