Dudley Donald Puppy is the protagonist of T.U.F.F. Puppy. He is a dim-witted and hyperactive mixed-breed dog who wears nothing more than a black shirt and has a habit of chewing his butt. Dudley is also quite gluttonous and childish. His catchphrase is "Hi gee gee." He is afraid of thunder and the dentist. He was voiced by iCarly cast member Jerry Trainor.
Kitty Katswell is the deuteragonist of T.U.F.F. Puppy. She is T.U.F.F.'s #1 agent. Kitty is also an expert in combat, weapons, and detective work. She is Dudley's partner, assigned to train him as a T.U.F.F. agent, but often finds herself and her skills foiled by Dudley's antics.
He is a creature of an unidentifiable species (later revealed to also be named Keswick) with a bad stuttering habit who works for T.U.F.F. Headquarters as their inventor and scientist. Keswick's brother-in-law is Stan.
The Chief is a tough but good-natured flea who runs T.U.F.F. headquarters. In "Internal Affairs", it's revealed that his real name is Herbert Dumbrowski, he has a bionic foot, and has short term memory loss.
Verminious Snaptrap, or simply known by his surname, Snaptrap, is the main antagonist of T.U.F.F. Puppy. He is the leader of the Diabolical Order of Mayhem, or D.O.O.M. for short.
The Chameleon is a major antagonist in T.U.F.F. Puppy who wants to get revenge on Kitty Katswell for putting him in jail (reasons unknown). He can disguise himself as any person or object using his transformation suit.
Bird Brain - Bird Brain is an evil criminal genius and mad scientist. He's a blue-bottomed booby who can't fly, so he uses gliders, cannons, and other flying contraptions he built, and has problems finding decent henchman to help him. He does have a little hummingbird ally named Zippy, who is completely oblivious to the fact that he can't fly and constantly tells him that he can fly if he believes.
Zippy - Zippy is a hummingbird that acts as Bird Brain's partner in crime. She is always trying to encourage Bird Brain that he can fly on his own as long as he believes. In Thunder Dog, she annoys Bird Brain a lot with her new catchphrase. She was the one who hired Bat and Owl. Zippy doesn't seem evil, so it is unknown why she is working with Bird Brain.
D.O.O.M. is the main villain organization in T.U.F.F. Puppy. It is lead by Verminious Snaptrap and usually commits crimes that involve world domination. It is located in the city of Petropolis, but its location seems to change a few times in the show, though it could be possible that D.O.O.M. has multiple entrances or HQs around the city.
Peg Puppy is Dudley's overprotective mom. She's a bit nervous about Dudley being an agent, but she wants him to do what makes him happy. Now, if he'd only wear pants…
