After much research, I have come up with the following criteria:
Europeans and Africans do not exist in the Avatarverse. By extension, neither do Latinos. Aboriginal Australians may not exist, either. Hopefully future series confirm this.
All characters must be Human. Homo Sapiens. No aliens, hybrids, mutants, or reincarnated alien hybrids.
No preexisting health conditions. Certain physical disabilities that do not make heavy exercise impossible are allowed, however. But if the character already has trauma, psychical or mental, they are disqualified.
The character must not be primarily motivated by the love of combat, competition, or martial arts. No blood knights or spirited competitors allowed.
If all else passes, the character must be family-friendly and be rated TV Y-7.
Cyborgs are allowed as long as they need their cyborg parts as disability aids. Anyone who is turned cyborg against their will or is more machine than human is disqualified.
For Dexter and Profesor, it comes down to how skilled they are at martial arts, or just unarmed combat.
Is this about James Cameron’s Avatar or Avatar the Last Airbender? I’ve never seen either one, but I’m guessing mine don’t since the two mains are gay and motivated by either vengeance or extreme pleasure seeking. ¯\_(ﭢ)_/¯
I can’t imagine the Professor doing martial arts XD I can imagine him failing though XD
But maybe the Mayor might fit the criteria… I don’t really like him but he’s the small-but-tough type of character. Especially when it comes to pickles.
Hmm… what about androids like Data? Data has, potentially, some ability to sort of maybe kind of feel or be human.