The cast page is mainly for those who hadn't seen avatar and can be skipped.
Kitiara Beifong - airbender
( I know that she looks like Suki, it is just the best appearance for her because I want her look like her mother, our beloved Lin Beifong )
Lin Beifong - earth and metal bender
Tenzin - air bender
Korra - avatar
Asami Sato - non bender
Bolin - earth and (later) lava bender ( Mako's brother )
Mako - fire bender
Two family trees for better understanding of the characters and their relationships :
Rohan is still a baby in the story.
Wei and Wing are twins.
Bumi was a non bender who started bending the air after the opening of the portals, same Opal.
Baatar Sr. & Jr. and Pema are non benders.
Jinora, Ikki, Meelo and Rohan are air benders.
Toph, Su, Wei and Wing are earth and metal benders. ( I think that I saw Huan bending metal also, but he mustn't be trained at combat )
Kya and Katara are water benders.
Su's full name is Suyin.
Kuvira - earth and metal bender ( villain of season 4 )
Zaheer - air bender ( he became like Bumi and Opal ) {main villain season 3}
Ghazan - earth and lava bender {villain season 3}
Ming-Hua - water bender (armless) {villain season 3}
P'Li - fire and combustion bender (Zaheer's girlfriend) {villain season 3}
Aiwei - earth and metal bender {helper of Zaheer and Red Lotus[ =Zaheer and his friends]}
Queen of earth kingdom, Hou-Ting - non bender
If someone new will be needed, I will add him later.