Korra

Avatar Korra is the main character in Avatar: Legend of Korra, and the successor to Aang as the Avatar. She is a teenager born to the Southern Water Tribe. At the start of Legend of Korra, 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 and an airbending master. During her training, she finds some anti-bending unrest in the city.[1] Not much else is known about her.

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.
 * 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.
 * 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.
 * As she is from the Southern Water Tribe, it is possible that she could be Sokka and Suki's granddaughter.
 * If she is Sokka and Suki's granddaughter that would make Tenzin either her mother's or father's cousin, so the already created fan-ship "Korzin" (Korra and Tenzin) would not be possible.
 * The ship seems even less likely because of the probable considerable difference in their ages, with Korra being in her teens while Tenzin is likely older (possibly as old as 72).
 * It is possible that she was raised in the Southern Water Tribe but was sent to the Northern Water Tribe to learn Waterbending, due to the fact the Fire Nation virtually eradicated Waterbenders in the Southern Water Tribe, when she was identified as the Avatar. 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.
 * 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,[2] this would mean Aang died somewhere in between 156-159 ASC and only lived to be biologically 69-72 years (chronically 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.
 * It could be a Polar Bear Dog if she does have one

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 (though not all Aboriginal languages as there many).
 * 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 Avatars death.