Aang is an airbender from the Southern Air Temple. He succeded Avatar Roku making him the avatar during the 100 year war. As an Air nomad, he believes that he shouldn't kill, both animals and people, even if it is to protect others.
Roku is a firebender from the Fire Nation. He succeded Avatar Kyoshi. He died right before the 100 year war started. He guided Aang through the Avatar state during the 100 year war.
Kyoshi is an earthbender from the Earth Kingdom. She succeded Avatar Kuruk. She died at 230 years old making her the oldest human.
Kuruk is a waterbender from the Northern Water Tribe. He succeded Avatar Yangchen. He hoped that he would be able to change the world and make it better.
Yangchen is an airbender from the Western Airtemple. She succeded Avatar Szeto. Although she was an Air Nomad, she would do anything to keep balance and peace in the world.