War changes the children of every nation

Character progression through the series:

Sokka at the beginning: Young boy trying his hardest to be a soldier and protect his people.

Sokka at the end: Brave, capable and trustworthy soldier. 

Zuko at the beginning: Banished prince trying to capture the Avatar.

Zuko at the end: New Fire Lord on the path of building a better future for his nation and the world.

Katara at the beginning: Young waterbender trying to master his element without any help.

Katara at the end: Waterbending Master.

Aang at the beginning: Goofy kid who likes to go penguin sliding.

Aang at the end: Fully realized Avatar.

Topt at the beginning: BADASS MOTHERFUCKER

Topt at the end: BADASS MOTHERFUCKER WHO CAN METALBEND