Unalaq

"You think what Avatar Wan did was good? Driving almost all the spirits from this world? The Avatar hasn't brought balance, only chaos. You call yourself the bridge between the worlds, but there shouldn't be a bridge. We should live together as one."

- Unalaq to Korra, reflecting his true motives

Unalaq was one of the main antagonists of Book 2; Spirits in the Legend of Korra, the others being the Dark Spirits, and Vaatu. He was Korra's uncle, the younger brother of Tonraq (Korra's father), and the father of the twins Desna and Eska. Though initially Unalaq seemed to be a well-meaning individual who offers to train Avatar Korra in the ways of the Spirits, his villainous side was revealed when it's learned that he was the one responsible for the banishment of his brother Tonraq from the Northern Water Tribe. His villainy becomes even more apparent when it is revealed that he is working for Vaatu. He was also the first (and only) Dark Avatar.

Past
Unalaq was the second child to be born to the Chief of the Northern Water Tribe, his brother Tonraq being the first. As he was growing up, Unalaq took a fascination towards the Spirits, as well as their ways. It was also revealed that Unalaq was always jealous of his older brother, Tonraq, and that he wanted to become the Chief of the Northern Water Tribe. So to become next in line, Unalaq devised a plan to get his brother banished. Unalaq hired a small army of Barbarians to attack the Northern Water Tribe. After the Barbarians managed to get Tonraq's attention, they were to retreat to a Spiritual Forest, to which Tonraq destroyed the forest to find them. Later that night, after Tonraq captured the Barbarians, angry Spirits attacked the Northern Water Tribe. With his knowledge of the Spirits, Unalaq managed to subdue all of them with ease. Afterward, Tonraq admitted to his mistake. Enraged, the Chief of the Northern Water Tribe, their father, banished Tonraq to the Southern Water Tribe. With his brother banished, Unalaq became next in line to become Chief of the Northern Water Tribe.

As years went by, Unalaq eventually became the Chief of the Northern Water Tribe, and eventually had two kids, Desna and Eska. He eventually found out that his brother was the father of the latest Avatar; Korra.

Becoming Korra's Teacher
Six months after Korra defeated Amon, Unalaq and his children came to visit his family at the Southern Water Tribe, while attending the Glacier Spirits Festival. He stated that he was disappointed on how the Southern Tribe forgotten about the Spirits, and certain traditional ways. During the Festival, Unalaq was attempting to convince Korra to be his student so he could teach her about the spirits, how to tame angry Spirits, and the Spirit World. But both Tenzin and Tonraq didn't want her to be taught by him. That night, an Angry Spirit attacked the festival. Korra and her friends were proven to be no match for the Spirit, but then Unalaq appears out of nowhere and managed to tamed the spirit. Impressed by Unalaq, Korra accepted his offer, much to her father's disapproval. Unalaq told Korra that in order to calm the Spirits, they would have to journey to the Everstorm to restore the Southern Lights. After a while, Unalaq, Korra, her friends and Tonraq reached the Spiritual Forest. Unalaq explained that she was the only one who could enter the forest.

Controling the Southern Water Tribe
After Korra successfully unlocked the portal between the Human World and the Spiritual World, Unalaq told her that it wasn't over yet. The next morning, Soldiers of the Northern Water Tribe arrived at the shores of the Southern Water Tribes. Unalaq told Korra that more work needed to be done before the two tribes were truly reunited again. While they were discussing this, the soldiers created blockades to prevent any citizen of the Southern Water Tribe from escaping, or anyone to enter the South Pole. This caused tension between the North and the South. Unalaq stated that all of this was necessary to unite the two tribes. One night, Southern Rebels attacked Unalaq in his sleep and attempted to kill him. Korra managed to rescue him and capture all of them. At first Unalaq was considering banishment for their crime, but Korra recommended a trial to the assassins, to which Unalaq agreed. The next morning however, Unalaq, along with a small group of Northern Water Tribe Soldiers appeared at the door of Korra's home. Unalaq stated that Tonraq and Senna were under arrest for attempted assassination.

The Trial
Korra's parents and the Southern Rebels were put on trial. Unalaq told Korra that he personally hired the "fairest" judge he could find; Judge Hotah. Despite this, all except for Senna were found guilty on for treason, and the crime of treason is punished by death. Enraged, Korra threated to kill the judge if he didn't change the sentence. With that gesture, Unalaq managed to "convince" the Judge to reconsider. With that, Hotah lowered the sentence to life in prison.

Unalaq Revealed
Later that day, Korra chased down Hotah and confronted him. He told her that the trial was rigged by Unalaq. He also told her that Unalaq did this so he could earn Korra's trust and get his brother out of the way. Hotah even said that Unalaq was responsible for Tonraq's banishment in the first place. After finding out, Korra and her friends went to Tonraq's prison cell to break him out, only to find out that his cell was empty. Just then Unalaq appeared and told her that both Tonraq and the rebels were sent away via a ship heading to the north. Confronting Unalaq about his selfish and underhanded deeds, Korra renounced him as her teacher and demanded that he recall the prison ship, reminding him that he still needed her to open the northern spirit portal. However, Unalaq confessed that he no longer needed her, revealing he had only been exploiting her into thinking that. This caused the Avatar to attack him out of sheer anger and fury. Both Korra and Mako confronted Unalaq, but Unalaq proved to be a powerful waterbender. After a while, Korra unleashed a powerful gust of wind to push Unalaq back. With that distraction, Korra and her friends ran off to save Tonraq and the rebels.

However, it was revealed that Unalaq still needed Korra to open the northern spirit portal. So he sent Eska and Desna to find and capture the Avatar alive. Upon learning of Korra's apparent demise at the hands of Dark Spirits, he was disappointed with his children's failure but also decided that they could open the Spirit Portal through other means.

Vaatu's Enforcer
It was later revealed that Unalaq is working for Vaatu, who told him that Korra was in fact alive and was coming for him in the Spirit World. Upon Korra's arrival to the Spirit World, Unalaq kidnaps Jinora (who had come with Korra), with a little help from Wan Shi Tong, and threatens to kill her and destroy her soul if she does not open the Spirit Portal for him, forcing Korra to open the portal. He then tries to kill Korra after she opens it but fails.

Shortly after the spirit portals were opened, Unalaq returned to the real world to fight off the remaining Southern Rebels. With the help of the Dark Spirits, Unalaq was able to defeat the Rebels, either by capturing them, or severally injuring them. However, Tonraq showed up in hopes he can defeat his brother. Despite his best efforts, Tonraq was easily outmatched by Unalaq. With the Southern Rebels out of commission, Unalaq focused on having both of his troops and the Dark Spirits guard the Southern Spirit Portal, knowing that Korra would show up to close the portal. Upon having nearly everyone captured, Unalaq reveals his full intention; he wants to merge with Vaatu so he can become a Dark Avatar, just as Wan had done with Raava. Tonraq begs him to reconsider, but to no avail.

Dark Avatar and Demise
Upon Harmonic Convergence, Vaatu was released, and merged with Unalaq to become a Dark Avatar. Upon a destructive battle between the two Avatars, Unalaq/Vaatu proceeded to rip Raava out of Korra, destroying both Raava and Korra's connection to past Avatars. He proceeded to Republic City where he would lay waste in order to bring about a new world order.

While seemingly unstoppable, Korra returned for a second battle with him as a giant spirit (much like Unalaq/Vaatu). During the battle, Jinora's spirit manifested inside Unalaq/Vaatu, creating (and pulling out) a small light that was used to recreate Raava. Raava and Korra then proceeded to use the spirit purification ritual on Unalaq/Vaatu, causing them to vanish.

Although Vaatu will eventually be recreated the same way as Raava, Unalaq is no more.

Powers
Unalaq is a powerful waterbender who also has the ability to calm spirits. He's one of the few male waterbenders that can use water to heal wounds. When Unalaq is in the Spirit World, he can corrupt human souls resulting in killing the human in the process.

Trivia

 * Unalaq is extremely similar to Councilman Tarrlok:
 * Both are charismatic male waterbenders with ambiguous motivations that claim to be well-intentioned
 * Both use their claims of being well-intentioned as a justification for oppressing others
 * Both manipulate Avatar Korra for their own ends
 * Both are the brother of another main character in the show (Amon and Tonraq respectively)
 * Both are similar in appearance
 * Unalaq is also similar to Fire Lord Ozai:
 * Both were ambitious power-hungry siblings who took a title of leadership that was originally intended for their brother.
 * Both are also arrogant and powerful benders.
 * Both delude themselves into being the face of a new era (Unalaq as the Dark Avatar, and Ozai as the Phoenix King).
 * Both gained their god-like powers from a rare event that occurs (Unalaq from Harmonic Convergence, and Ozai from Sozin's Comet).
 * Both used their own families to further their own goals.
 * Both their sons (Desna and Zuko respectively) start out wanting to please them, only for them to turn against their fathers and help defeat them.
 * Likewise, both their daughters (Eska and Azula respectively) possess a cruel, sadistic streak.
 * If Unalaq had not gotten his Brother Tonraq banished from the Northen water tribe, then Tonraq would have never married Senna and Korra would have never been born and the next Waterbending Avatar would have been someone else.