Unalaq

Unalaq is a character from Avatar The Legend of Korra

History
Unalaq was a waterbending master, the chief of the Northern and Southern Water Tribes,[6] a former member of the Red Lotus, and the first and only Dark Avatar. He was the younger brother of Tonraq, husband of Malina, with whom he fathered Desna and Eska, and uncle of Avatar Korra. A particularly spiritual man, he briefly served as Korra's spiritual mentor until her discovery of his involvement in her father's banishment, at which point he was absolved as her teacher and shunned.[7] Unbeknownst to anyone, Unalaq was working to release Vaatu from incarceration in the Spirit World, and succeeded in this task before fusing with Vaatu to become the Dark Avatar. To this end, Unalaq nearly destroyed Republic City before being defeated and killed by his niece. Even though his attempt to destroy the Avatar and usher the world into an era of darkness was consequently thwarted, Unalaq succeeded in reuniting humans and spirits and thus changing the world forever.[3]

More Information: http://avatar.wikia.com/wiki/Unalaq