Dr. Krank is first seen on "The Barry Anger Show" where the host interviews him and he says he can turn animals into human beings. Spot finds this as the opportunity to live his dream and goes to see him.
Spot and Leonard meet up at a gas station. Through many quick costume changes, Spot fools Mrs. Helperman into believing that he is Scott Leadready II and that his family, en route to Sunny Southern Florida, had to return home, but he could still go with the Helpermans. Spot, Leonard, and Mrs. Helperman continue on their way to Florida, singing through all fifty states .
Meanwhile, back at the Helperman residence, Pretty Boy and Mr. Jolly, see another episode of Barry Anger in which Anger reveals that Krank cannot turn animals human, but rather into ugly, terrifying mutant creatures. They decide that they must track down Spot and stop him from being turned into a monster, but Mr. Jolly is afraid to leave the house. Pretty Boy assures him that they can be tough despite their size.
When Spot and Leonard find Krank's lab, he tries to turn a frog into a human but he only makes it 'moo'. Spot arrives and convinces Krank to not destroy the machine and that he needs a mammal to make a man not swamp creatures.
Spot is turned into a human but instead, he's turned into a man not a boy (his age in dog years). Krank then traps Spot and Leonard in a cage to turn them into media freaks.
Then, his nephew, Ian arrives and sets them free in exchange for a chew toy. When Krank finds out, he grounds Ian for the rest of the summer and traps him in a web. He also sends his minons Dennis and Adele to capture Spot.
Later, when Ian calls his parents to take him home, Krank tells him to stay off the phone (he wants to call out for a pizza).
The next night, Leonard arrives at the lab to turn into a dog to be with Spot, but Krank uses him as bait. Suddenly, Spot, Pretty Boy, and Jolly arrive in time to save Leonard. Spot installs the nickel Krank gave him earlier in the machine and it turns him into a mouse and Jolly chases him out of the lab.
When Spot is turned back to a dog, Jolly eats the mouse-formed Krank, therefore killing him and Ian decides to take Dennis and Adele as his cousins.
He's the first Teacher's Pet character to die and get eaten.
Kelsey Grammer, who voiced Krank also voices Sideshow Bob in the Simpsons.
He was originally going to look like the evil scientist from the Looney Tunes episode, Water Water Every-Hare and the bit more of a character that inspired Danny DeVito.