Katara and Sokka
Katara is a nice, pretty girl from the Southern Water Tribe. She was the last waterbender there-no one else there can control water with their minds. She is Aang's waterbending teacher and even eventually his girlfriend. A long time ago, when Katara was a little girl, the Fire Nation came and demanded the Southern Water Tribe to give them their last waterbender. Katara's mother, who couldn't control water with her mind, but knew Katara could, claimed that she was the waterbender. The Fire Nation took Katara's mother away, and Katara was forever after pretty angry with the Fire Nation soldier who captured her mother.
Sokka is the funny and sometimes annoying brother of Katara. He is a skilled warrior, and uses a boomerang for a weapon. Take away his boomerang-he gets REALLY mad! But, he's always there to protect his friends.