His daughter, on the other hand, is vocally related to another not quite sane person - while they usually sound different enough, compare Azula's "favorite Prisoner" speech in Black Sun day to Jeanette's comment how her father "died with a smile on his face".
Scott Menville (Robin, Ma-Ti) is a representative of one of the two tribes looking to cross The Great Divide, as well as one the guys who hit on Ty Lee in The Beach. ** Professor Chang is one of the monks who tells Aang he is the Avatar.
What Could Have Been: Toph was originally conceived as a guy. Variants of her original character model makes a few appearances throughout the series in bit roles, most notably as a bender in the show's opening sequence (Roku's Earthbending teacher) and THE BOULDER!
Word Of God says that the screechy actor who played her in the play is a flanderized version of her original character design. Aspects of her original male visual design and characterization were later incorporated into Bolin.
Zuko's great-grandfather is Avatar Roku — therefore, via Reincarnation, Aang... sorta. Technically.
Waterbending is the only bending skill that was not learned from an animal. Waterbenders are said to have learned from the moon; in contrast, earthbenders learned from the badger-moles, airbenders learned from the sky bison, and firebenders learned from the dragons. The entire concept is awfully similar to animal-based martial arts in Real Life, made famous by Hongkong martial arts movies like Jackie Chan's Snake in the Eagle's Shadow or Tiger and Crane Styles (best known for being edited into Kung Pow!.)
As mentioned on the main page, the bending styles themselves are based on actual Chinese martial arts (Waterbending is Tai Chi, Earthbending is Hung Gar, Firebending is Northern Shaolin Kung Fu, Airbending is Ba Gua). Exceptions not covered are:
Toph's own Earthbending style, taught directly by the badger-moles, is actually based on Southern Mantis style
Metalbending, based on Xing Yi Quan, which quite appropriately was developed in captivity as well
Bloodbending, based on Qin Na Shou, which was also quite appropriately a grapple-based technique
Redirecting lightning is the only style taken from a sword technique, the obscure Tai Chi sword discipline
You can probably catch some differences between Katara and Pakku's waterbending styles, since Southern and Northern are legitimate Tai Chi variants.
"Katara" means "curse" (both as in "hex" and "swear") in Greek. Of course, this is just a weird coincidence, but it is too odd to not mention. One would suspect that the character was so named because a Katara is a kind of Indian dagger, though.
A Katar is a type of Indian dagger.
The benders shown in the opening titles are actual characters from the show: Master Pakku for water, Azula for fire and an unknown male character for air.
Although the earthbender was Toph's original design, but when her design was changed, that design inspired later characters The Boulder, Sud (Roku's earthbending teacher) and "The Ember Island Players"' Toph (directly taken from that design).
Some argue that the airbender in the opening is Monk Gyatso. Others claim it's an older Aang (a theory largely debunked by the confirmed older Aang in the opening to The Legend Of Korra, who looks much different), and still others suggest it might be one of the unamed monks from "The Storm".
