4000+ characters

Most comedy shows can sometimes screw up the character by having him act too warm and naive and then too cold and mischievious. Which is realistic sometimes, but makes for a dumb confused character who doesn't know his own identity, standards, beliefs to feel confident in.

Sokka in Avatar for example was the resourceful straightman with a plan. He wasn't just a dumb comedy relief or a sarcastic pseudo intellectual, he could manage his own and played an important part in the show despite being powerless, hell
Katara was mostly abilityless in the first season.

For Katara...she was easy to anger because her hopes would get crushed and she was always expected to do everything by herself as the responsible mom figure of the group. Hence she tolerates Sokka's annoying demeanour, Toph's lazy irresponsible self, Aang's childlike behaviour. She is blunt, direct and that can make her very cold and indifferent when it comes to being sensible with what she's saying, hence why she can be a total asshole when she wants to. She isn't the shy type that cries over small stuff and comes off as overly caring of others feelings, more like that parent figure that scolds you She didn't act giddy, funny and all that extroverted and she would bottom up her feelings till they exploded.

Zuko was the cognitiviless opportunistic loser that would talk out of nowhere and wouldn't think things through. Hence he was a miserable person that would act angry to hide his insecurities, hence he would get angry at his own failures and upcomings in a defeatist kind of way, unlike Katara which gets overly determined and hopeful to get stuff done like her resppnsibility tells her to.
He was also very confused with his morality, standards, beliefs which made him a very stupid character, probably one of the reasons why he was so dumb at everything and lacking the cognitive talent improve on the go. Zuko's personality is 1 dimensional(stupid and simplistic, he'd parrot what others say after his reformation), but he's realistic despite his loser personality. Most people are confused, easy to misguide by others and start coping with their lifestyle till they find a new opportunity to grab desperately, despite it not being what they really wanted.

He learns what he really wants and goes after it. I only wish they focused more on the fact he got banished in the first place for caring too much about using the fire nation soldiers as cannon fodder.Most comedy shows can sometimes screw up the character by having him act too warm and naive and then too cold and mischievious. Which is realistic sometimes, but makes for a dumb confused character who doesn't know his own identity, standards, beliefs to feel confident in.

Azula was the perfectionist-obsessed student that would grow sociopathic and uncaring of others good will, hence controlling Mai and Ty Lee. She'd keep up improving and obsessively maintain her perfection to look good in her father's eyes and not end up banished like Zuko.

The rest of the secondary characters are just... too stupid and plain to even discuss. Toph is just that boisterous mischief-seeking kid that tries to act tough to hide the fact she's a timid little girl. A kid who couldn't wait to leave her parents home seeking adventure and to prove herself. She can sometimes act civilized because she lived in a royal palace, but she's such a simplistic stereotype that nothing breathes and comes off as natural like Aang. Toph even has crushes on Sokka for no good reason just because he's older than her. She questions Katara's authority because her stereotype tells her to be a rebel. Despite all that she is still a little girl and she gets angry and scared like an unexperienced timid girl. But her tomboy personality is so contained and forced that it's plain obvious she's written as a boring undeveloped kid going through a phase.

These are all realistic traits off real life experiences. Which means there's no real unique trait in these characters like something gene inherited and mentally complex.
What I said about the secondary characters.. their traits are dictated by their stereotypical traits rather than their life experiences, which makes them so shallow.

And I dabbled long enough. I'll stop posting now before a real writer gives me class on depthful characterization.