Naga

"water"

- Your best friend is a, uh, polar bear dog...? Somehow that makes perfect sense.

Naga is a polar bear dog that came into the possession of Avatar Korra as her companion, animal guide, and main mode of transportation. Despite her intimidating appearance, she is described as a "sweetheart" and is regarded as Korra's best friend. Undyingly loyal, she is very protective of Korra and has learned how to use her strength to help Korra out of perilous situations.

History
At some point, Naga met Korra and became her animal guide. Korra rides Naga like a horse, even into battle, where the animal proves to be quite agile, able to dodge moving cars at high speed and move quickly enough to keep up with them.

Naga later accompanied Korra when the Avatar escaped to Republic City, where the polar bear dog was seen catching fish from the pond in the city's park. As the guard came running, telling Korra not to fish, the Avatar escaped on Naga. She later helped Korra evade arrest by the Metalbending Police Force, but she and Korra were eventually captured and sent to Police headquarters.

While attempting to find Bolin, Naga was capable of sustaining a fast pace while chasing an Equalist convoy consisting of a truck and motorcycles. When Korra and Mako had their chi blocked and found themselves surrounded, Naga bit through her bindings, and she and Pabu scared the Equalists away, allowing the two to escape.

While Korra and Bolin were enjoying dinner at Narook's Seaweed Noodlery, they were approached by Tahno. He and Korra began trash-talking, and the pro-bender tried to provoke the Avatar into a fight. Since the Fire Ferrets would be disqualified from the Pro-bending Tournament if she were to lay a hand on him out of the arena, the Avatar called Naga instead, who intimidated the Wolfbats' waterbender with a loud growl.

When the Fire Ferrets found out that Amon had threatened the United Republic Council to shut down the Pro-bending Arena or face severe consequences, the team rode on Naga to City Hall so they could speak with the council.

The polar bear dog refused to carry Mako, Bolin, Asami, and Korra when they decided to patrol the city, forcing them to take a Satomobile. Korra later rode on Naga to the City Hall to face Tarrlok. Although concerned, Naga complied to Korra's order and waited outside.

Trivia

 * Korra and Naga greatly resemble San from Princess Mononoke and her wolf foster-brothers and foster-mother, the wolf goddess Moro, in both posture and physical traits. The creators admitted to having been inspired by Hayao Miyazaki's movie when creating Avatar: The Last Airbender.
 * Naga was based off the original early concepts of an anthropomorphic polar bear dog traveling with Aang that eventually evolved into Appa.
 * The kangal, which is a breed of dog in the real-world, served as a partial reference for Naga.
 * Naga is the Sanskrit and Pāli word for a deity or class of entity or being, taking the form of a very great snake in Hinduism and Buddhism.
 * Naga is an anagram of Aang.
 * Naga is the first known polar bear dog to ever be tamed.
 * While both of the known animals that precede Naga in the position of guide to the Avatar were the animals that their people learned their bending art from, Naga is just a regular animal, though this had to be the case since the Water Tribes learned waterbending from the Moon and Ocean spirits.
 * The symbol on Naga's chest is the same symbol that Tonraq wears on his chest.
 * Naga is modeled after the creators' dogs, who are both brothers.