Kuruk was the Water TribeAvatar immediately succeeding Avatar Yangchen and preceding Avatar Kyoshi. Native to the Northern Water Tribe, he was born around 345 BG and died in 312 BG. Though gifted as a bender, he was a brash and arrogant person, who always preferred a "go with the flow" kind of mentality. Due to this attitude and his pompous demeanor, Kuruk lost his fiancée, Ummi, to Koh the Face Stealer.
Living in a world brought to peace and stability by his predecessor's tenacious efforts, Kuruk spent most of his days searching both the physical and Spirit World for worthy opponents to challenge in bending contests, usually for no reason other than entertainment and pleasure. He also liked to show off grand displays of his bending ability to others, especially beautiful women. Kuruk airbent lotus tornadoes for young Air Nomad nuns, would challenge random Fire Nationcitizens to an Agni Kai, and engaged in earth-lifting contests with earthbenders. His strength in sparring matches was considered legendary, and no bender was ever able to trump his abilities. Kuruk was a "go with the flow" type of Avatar. The world's tranquility allowed him to step back from his responsibilities as the Avatar and let the four nations resolve their own conflicts. Although there was peace in his era, Kuruk's carefree lifestyle would eventually cost him dearly.
Never having even the slightest thought of settling down, Kuruk carried on with his casual way of life until the day he met his true love. At the New Moon Celebration, a festive meeting of the two Water Tribes, he met a woman named Ummi from the Southern Water Tribe. Kuruk fell in love with her at first sight and presented Ummi with a customary betrothal necklace shortly after their meeting, which she accepted. The two designated their marriage to be at the Spirit Oasis.
As they approached the altar on the night of their wedding, Ummi fell into the oasis, pulled in by an unseen force. She had been lured to the Spirit World by Koh the Face Stealer, to punish Kuruk for his past arrogance. Every year, on the anniversary of their wedding, Kuruk traveled to the Spirit World in hopes of saving Ummi, but failed on every occasion. His attempts made Koh hold a grudge against the Avatar. He eventually managed to find the spirit and would have slain him, were it not for his realization that the spirit had stolen Ummi's face and thus trapped her forever; he could not kill Koh without killing his wife in the process.
Appearances in Aang's life
Aang first learned about Kuruk while he was in the Spirit World during the Siege of the North. Koh informed him that Aang had attempted to slay him in a previous life, though the spirit never specifically identified this man as Kuruk.
Aang finally learned Kuruk's name when he was in a coma after Azula's lightning attack in Ba Sing Se. When they met in the realm of Koh, Kuruk asked Aang if he had seen a beautiful woman with long, brown hair. Aang responded by inquiring about Kuruk's dilemma, at which point Kuruk proceeded to tell him his history as the Avatar. After the tale, Aang realized that during his encounter with Koh, one of the spirit's faces was that of the woman Kuruk had described. Heartened by the knowledge of his wife's whereabouts, Kuruk set off to track down Koh once again. However, as Avatar Yangchen had predicted, Aang retained no memory of this encounter.
Later, Avatar Aang meditated, contacting Kuruk so to ask how Fire LordOzai could be defeated without killing him. Kuruk told Aang to actively shape both his destiny and that of the world, as the former had failed to do so in his own life. It was Kuruk's own arrogance and inaction that had cost him his beloved wife, Ummi. Aang took this to mean that Kuruk, like the other Avatars, believed it was necessary to use lethal force in order to protect the world. However, Kuruk's answer was much more open to interpretation, since "actively shaping your destiny" could have various meanings, including Aang's decision to strip Ozai of his bending.
Appearances in Korra's life
Kuruk stood alongside all the other Avatars when Aang passed on the knowledge of energybending to Korra and restored her bending, representing the newly established connection she made to her spiritual self.
After Korra lost her memory, Kuruk appeared before her, taking over from Avatar Kyoshi, and informed the young Avatar that she would have to return to the beginning to find Raava and reconnect with her Avatar Spirit.
While Unalaq was attacking Raava, Korra envisioned Kuruk as part of the Avatar lineup, which she had seen prior to regaining her bending; however, his connection to Korra was severed due to Unalaq's assault on and subsequent destruction of the light spirit.
In the last episode of the first series, Kuruk was seen in Aang's vision before he entered the Avatar State.
During his airbending training, Avatar Kuruk was seen with customized Air Nomad clothing that was similar to Aang's, but in varying shades of blue.
Kuruk is the Pawnee Native American word for "bear", mimicking how Kuruk is frequently seen wearing an animal pelt resembling a bear-like creature over his head.
Koh stated that Kuruk attempted to slay him some eight or nine centuries prior to the episode, but for that to have happened, he would have had to be older than his immediate successor, Avatar Kyoshi, who was the oldest Avatar in history.
Kuruk's favorite mode of transportation was by sea, surfing on a raft using waterbending.
Kuruk is, so far, the only known Avatar whose predecessor and successor were both women.
Among all Avatars with a known lifespan, Kuruk lived for the shortest period of time. Ironically, his successor, Kyoshi, lived longer than any other Avatar.
Kuruk is the most recent Avatar who has not had to deal with a large scale conflict during his time. Kyoshi ended the War of Chin the Conqueror, Roku and Aang were faced with the prelude and conclusion of the Hundred Year War, respectively, while Avatar Korra was faced with the Water Tribe Civil War.