Hundun is the main antagonist of the Avatar: The Legend of Korra video game.
Hundun has been an enemy of the Avatar for 1,000 years. He was a tyrant king that one of Korra's past lives defeated and mortally wounded his conjoined twin in the process. Hundun and his brother escaped through meditation, but were trapped in the spirit world which filled them with an unrelenting hatred towards the Avatar.
Hundun spent centuries searching way to exact his revenge on the Avatar and discovered a way that would allow him to absorb the Avatar's chi so he could restore himself and his brother and would make them immortal. When Korra decided to leave the spirit portals at the north and south pole open after Harmonic Convergence, Hundun's spirit was able to reenter the physical world and thus put his plan for revenge into motion. He was able to gain access to the vast fortune he acquired from his time as a king and used it to recruit the Triple Threat Triad, then he used his charisma to recruit what remained of the Equalists and finally using his mastery of the Chaotic Attack to summon hordes of Dark spirits; with that he had an army to attack his ancient enemy with. He approached Korra when she was alone and used Chi blocking techniques on her, forcing Korra to relearn her Bending arts one by one as she fought Hundun's forces though Air Temple Island, Republic City, the south pole and the spirit world.
Korra confronted Hundun at the Tree of Time were she learned of their last battle 1,000 years ago and was able to fully undo Hundun's chi blocking and renter the Avatar state. Hundun and his brother proved to be formidable opponents with their strength, speed, earth bending and ability to draw on dark energy that enabled them to teleport, increase their size, stretch their limbs, create barriers, release blasts of energy, cast illusions and summon their remaining dark spirits to aide them battle. In the end however Korra was able to defeat Hundun and his brother and use spirit bending on them causing her two enemies to dissipate.