Hundun

"spirit"

- I am known by many names ... but you may call me Hundun, Master of the Chaotic Attack. In my time, I was a king." "Huh ... and now you're just a sad old man." "Yes ... but one who still has much treasure in the physical world; treasure enough to buy an army. And thanks to you opening the portals, now they can march right in.

Hundun and his brother are ancient enemies of the Avatar. They wish to throw the world into chaos and were enemies of Korra's after she opened up the spirit portals, once more connecting the physical and Spirit Worlds.

History
Hundun and his conjoined twin fought against an incarnation of the Avatar a thousand years ago, during that confrontation Hundun's brother was badly injured and they have lived in the Spirit World ever since then. After the Harmonic Convergence, they entered the physical world again and began pursuing their goals of bringing chaos to the world. Hundun used dark spirits under his control, Equalists to whom he had promised a new world order and the Triple threat Triad, which was paid with treasures Hundun had hidden in the physical world during his lifetime. They were stopped by Korra less than two weeks after entering the physical world.

Trivia

 * Hundun is named after a Chinese chaos entity.