Korra

Avatar Korra is the successor to Aang as the Avatar. She is a teenager born to the Southern Water Tribe. She has already mastered Waterbending, Earthbending, and Firebending, and only needs to learn Airbending and control of the Avatar State to become a fully realized Avatar. Seventy years after the end of The War, Korra journeys to Republic City seeking the tutelage of Tenzin, the son of Aang and Katara as an Airbending master. During her training, she finds some anti-bending unrest in the city. Not much else is known about her.

Confirmed Facts

 * Korra is from the Southern Water Tribe.
 * She has already learned and mastered Waterbending, Earthbending and Firebending.
 * She is the Avatar after Aang.
 * In a flashback, 5 year-old Korra will be played by Dee Bradley Baker's daughter, Cora.

Rumors & Speculation
'Note: PLEASE note that the below "confirmations" delivered to you by many Avatar fansites are NOT confirmed as of yet. DO NOT take most of the information here as a fact. Also, DO NOT edit things interpreted as "fact" into this article. Furthermore, do not add in "questions" and speculation debates.'

The story has been confirmed. Has been revealed at Comic-Con 2010 (see confirmed facts).
 * Korra_copy.png recently leaked unconfirmed line test animation from a Korean studio shows what appears to be Korra battling several opponents. In this, she exhibits mastery over several fighting styles, and performs moves similar to those of previous characters.
 * In this clip, Korra is seen incapacitating an enemy using a technique similar to Chi Blocking.
 * Korra is also seen performing the same move Zuko used to destabilize Azula during their Agni Kai.
 * Aang will mentor her from the Spirit World, just as Roku mentored Aang.
 * This seems highly likely if Aang's own experiences are any guide. Aang immediately felt a strong connection with a statue of Roku, instinctively knowing Roku's name and that Roku was his previous self, and Roku appeared to Aang more regularly then any other of his previous selves.
 * Also, since Aang was the most recent Avatar before Korra, any of his wisdom will be the most relevant to Korra, and the time periods in which they kept balance are very close to each other.
 * In theory, Korra is the spiritual parent of Tenzin, seeing as she is the new Avatar. Since Korra was Aang in the past life, that would technically make her the parent of Tenzin in a spiritual sense.
 * This relationship is similar to how Aang is related to Zuko and Azula (spiritually) due to Aang being Avatar Roku in the past life.
 * It is possible that she was raised in the Southern Water Tribe, but was sent to the Northern Water Tribe to learn Waterbending when she was identified as the Avatar, due to the fact the Fire Nation virtually eradicated Waterbenders in the Southern Water Tribe. However it is also possible that, thanks to Master Pakku's efforts to rebuild the Southern Water Tribe, she was raised and taught in the Southern Water Tribe.
 * It is also possible she was taught Waterbending by Katara.
 * Korra is likely between 16 and 19 years old judging from the picture and the tradition of revealing the Avatar at the age of 16. As the series is set 75 years after The Last Airbender, this would mean Aang died somewhere in between 156-159 ASC and only lived to be biologically 69-72 years (chronologically 169-172 years) if he were 13 when the series ended, or 68-71 years (chronologically 168-171 years) if he stayed 12 throughout the whole series.
 * It is unknown whether Korra will have an Animal Guide, like Appa was to Aang or Fang was to Roku.
 * The book "The Art of the Animated Series" depicts several early concepts of a large Polar Bear Dog. The notations describe the creators' love for the idea of the dog, but also states that they were unable to use him in the first series, but then go on to hint that, "We have a feeling he'll turn up somewhere," hinting that the Polar Bear Dog will make an appearance in Avatar: Legend of Korra.

Trivia

 * Korra is a word of Greek and Irish origin meaning, "from the mountain valley". It also means "maiden" in Greek, and "grass" in Aboriginal (Native Australian) language.
 * Korra is pronounced the same as the Irish (Gaelic) word "cora" which translates as "weir".
 * Korra is also the name of a village in the Tibet Autonomous Region of China.
 * Her name follows a long line of tradition in the Southern and Northern tribes, where often people include one or two "K"s and have an "UH" sound in their name. (Katara, Hakoda, Sokka, Pakku, Kya, Kuruk, Kanna, Arnook, etc.)
 * According to Avatar Extras, Aang was born at the exact moment of Roku's death, but Avatars can be born up to a week after the previous Avatar's death.
 * Korra is between 16 and 19 years of age.