Vaatu

"See you at the end of the world."

- Vaatu to Wan "I lived ten thousand lifetimes before the first of your kind crawled out of the mud. It was I who broke through the divide that separated the plane of Spirits from the material world. To hate me is to give me breath. To fight me is to give me strength. Now prepare to face oblivion!"

- Vaatu to Wan

Vaatu is the Spirit of Chaos and Darkness and the true main antagonist of Book 2: Spirits in The Legend of Korra''. ''He fought the first Avatar Wan 10,000 years ago and attempted to rule the world and is the source of all evil and darkness in the Avatar world.

History
Vaatu first appeared engaged in battle with his opposite number Raava. Attracting the attention of a then wandering Wan, Vaatu convinced Wan that Raava was the instigator of the conflict and was oppressing him. Falling for his ruse, Wan freed Vaatu from Raava's grasp, allowing him to flee. Once freed, Vaatu wasted little time corrupting Spirits and turning them into Dark Spirits, also planning to cause 10,000 years of darkness on Earth.

Wan, realizing his mistake, tried to help Raava defeat Vaatu and the two traveled the world, with Wan learning all four elements so as to better help Raava fight Vaatu. With Raava's help, Wan was able to master them all. Unfortunately during that time, Vaatu had been harnessing the Spirit's anger to become stronger while simultaneously making Raava weaker, also creating more and more Dark Spirits.

Raava explained that in a year, Vaatu would use the Harmonic Convergence to make Raava disappear forever and allow him full power. When the time of Harmonic Convergence came, Wan engaged Vaatu in battle, but Vaatu was far too powerful to be defeated. Raava entered Wan's body and the fight resumed, only for Vaatu to triumph anyway. At that moment the Harmonic Convergence occured but before Vaatu could complete his plan, Wan used the Harmonic Convergence to merge Raava with his soul forever, making Wan the very first Avatar. Wan was able to then seal Vaatu in a tree and sealed away the Spirit World, putting an end to Vaatu's threat for 10,000 years.

However, as of The Legend of Korra, Vaatu has made efforts to bring to about his return, corrupting Spirits into Dark Spirits and also enlisting the help of Unalaq to free him. Unalaq has convinced Korra to open both the Northern Portal and the Southern Portal, and so upon Harmonic Convergence, Vaatu not only escapes, but also merges with Unalaq to become the first Dark Avatar.

Unalaq/Vaatu proceed to attack the Avatar, rip Raava out of Korra, destroy Raava (temporarily, as one cannot exist without the other), and attack Republic City. When Korra faces them a second time, Jinora's spirit pulls a small light out of Unalaq/Vaatu, recreating Raava. Raava and Korra merge once again, performing the spirit purification ritual in Unalaq/Vaatu, causing them to vanish.

Since one cannot exist without the other, Vaatu will eventually be recreated the same way Raava was. His host (Unalaq), however, remains deceased.

Vaatu returned in Book 3: Change as one of Korra's hallucinations. When Korra was poisoned by the red Lotus, Korra hallucinated Ming-Hua turning into Vaatu, which later floats up to Korra's face, telling her she is too weak to resist the poison and he is stronger then ever. Emphasizing the futility of her resistance, he urged her to just let go and enter the avatar state.

Mortal Enemies

 * Raava: His polar opposite who fused with Wan and every Avatar afterwards. Out of revenge, he destroys Raava, ensuring that the Avatar would be too helpless to defeat him. Later, she returns just in time as Korra manages to defeat him.
 * Wan (First Avatar to defeat him)
 * Korra (Bane of his existence)

Trivia

 * Vaatu's backstory, role, and physical appearance bear some resemblance to Aku, who's voice actor Mako also voiced another Avatar character, Iroh.
 * Vaatu has many similarities with Malware from Ben 10: Omniverse.
 * Both have the same color scheme.
 * Both have the ability to fire an eye beam.
 * Both are beings that corrupt others.
 * Both were hidden main antagonists who had major henchman act in their place before revealing themselves; Malware had Khyber work for him to bring Ben to him, while Vaatu had Unalaq carry out his plans for him so that he could be freed in time.
 * Both Vaatu and Malware ripped out and destroyed an entity from the main hero whom they considered a major part of them; Vaatu ripped out and destroyed Raava from Korra while Malware destroyed Feedback after ripping him out of Ben. Both Ben and Korra felt traumatized and saddened by this event.
 * They both took on giant forms and laid waste to a city.
 * Both ended up having the hero they each destroyed emerged from them; Jinora extracted Raava from Vaatu while Feedback emerged from Malware.
 * Both were destroyed by energy attacks.
 * Vaatu seemed very similar to The Architect from The Matrix due to his beliefs on life and that he has a polar opposite, Raava and The Oracle respectively.
 * He bears some similarities to Hexxus from the 1992 animated fantasy film by 20th Century Fox, FernGully: The Last Rainforest.
 * Both are shadowy monsters possessed of apparent immortality who though locked away for centuries inside a tree eventually return to bring ruin and destruction to the world once more, as well as coming into a conflict with a female hero and taking sadistic joy in defiling and corrupting things that were once good (for Hexxus nature and for Vaatu Spirits). Finally, neither one can be outright destroyed for good, only imprisoned or otherwise prevented from doing more harm.
 * Tathamet, the original Prime Evil in from Diablo video game series is very similar with Vaatu though there are also difference between them as well aside being a Bigger Bad in each franchise they featured at:
 * Similarities with Tathamet:
 * Much like Tathamet and Anu, Vaatu was trapped in a brutal conflict with Raava in the past before mankind born.
 * Both Vaatu and Tathamet mainly represent Chaos and Darkness.
 * Both Vaatu and Tathamet has powers to corrupt other beings to their side (Spirits for Vaatuu and mortals and some angels for Thatamet). Although, Tathamet's fullest extent of corrupting powers are shown in Diablo 3, where with help of Zoltun's Black Soulstone and his sibling's essence, Diablo gained both aspect and powers of Tathamet, and use the said powers to corrupt newborn angels and turn them into abomination that immediately locked up during his siege in Heaven. Despite this, as separate entity, Tathamet's essence (better known as Prime Evils and Lesser Evils) still retain their corrupting powers, able to corrupt some humans to their side, like Vaatu did to spirits.
 * Both Vaatu and Tathamet's essence can merged with a human body, in which can affect their powers.
 * But there are few things that made Vaatu and Tathamet apart as well:
 * Vaatu can resurrect himself wholly after being destroyed, while Tathamet cannot, as Tathamet's essence split into demons with his aspects becomming the Prime Evils Mephisto, Baal, and Diablo and Lesser Evils Andariel, Duriel, Belial, and Azmodan.(Though interestingly The Prime Evils and Lesser Evils can resurrect themselves after they die) And rest of it's essence transformed into Hell since his destruction.
 * Vaatu and his light counterpart Raava is a separate entity in spite of being related, while Tathamet and Anu used to be a single being.
 * Vaatu and Tathamet's final fate after their conflict with their light counterpart was very different. While Vaatu was initially imprisoned, and later purified and likely returned in the future, Tathamet and Anu effectively destroyed each other, though their separated essence still fought each other.
 * He is voiced by Jonathan Adams, who has voiced several other villains, including Dormammu, who Vaatu is similar to.
 * Vaatu and Raava appear respectively to be representations of the yin-yang (Taìjí tú) concept in Chinese philosophy, which is used to describe the way in which opposite forces are interconnected and interdependent in the natural world. In this case, the concept accounts for the duality associated with the fact that Vaatu represents darkness and chaos, while Raava represents light and peace. His attributes, however, are ironically closer in Taoist thought to the ideal of light (yang) than that of darkness (yin); Vaatu is male and aggressive, as opposed to female and calm.
 * Furthering the yin-yang comparison, Vaatu and Raava are said to contain vestigial elements of each other within themselves, from which they can regenerate after being defeated. Similarly, each side of the yin-yang symbol bears a small dot of the opposite color, symbolizing how each side bears a part of the other.
 * This duality is also apparent in their names and color schemes. In Sanskrit, vatu (वतु) means "silence", which is the opposite of rava (रव), which means "sound". The two spirits are also negative images of each other.
 * Vaatu and Raava are also comparable to the Zoroastrian concept of moral dualism, Vaatu being similar to Ahriman/Angra Mainyu in representing darkness and immorality.