La

La, the Ocean Spirit, is one of two spirits which resided at the Spirit Oasis at the North Pole, in the Northern Water Tribe's capital city.

History
Thousands of years ago, La and its counterpart Tui decided to manifest themselves in the physical world as to benefit mankind, taking up residence in an alcove of the Northern Water Tribe's capital city. Thus, the Spirit Oasis in the city became its most treasured landmark and most defended point.

Over the ages, few have known the Ocean spirit's true identity. But when Admiral Zhao looted Wan Shi Tong's library, he discovered that the Ocean was actually a koi fish. He kept this knowledge a secret for years, knowing it would provide him a strategic advantage if he ever invaded the North Pole.

The Fire Nation launched a siege on the capital city of the North. Steadily, the Fire Nation navy advanced upon the city, eventually destroying its protective locks and dams and advancing onto its white marble surface. Admiral Zhao advanced with his personal guard to the back of the royal palace to kill Tui. In a scoop, Zhao caught Tui in a bag of water, and a lunar eclipse occured, destroying the power of the Waterbenders worldwide. To the horror of Katara, Aang, and General Iroh, Zhao then kills Tui, destroying the moon altogether. Iroh, in anger, lashes out at Zhao, killing his guards. Aang then enters the Avatar State and enters the water with La. The two fuse together and become one giant "water monster." Fused together, they destroy all the fire navy ships and kill Zhao.

Although Tui is dead, Yue later sacrifices herself to it, becoming one with the Moon Spirit.