The Perfectionist is a villain who appears in Perfect and the final antagonist Courage faces in the series. She is an elderly woman who teaches people to be "perfect". When Courage was going through the day of doing things wrong, she came to the farmhouse (with Muriel and Eustace unaware of her presence) to strictly train Courage to become "perfect".
The Perfectionist had Courage enroll in various "perfection lessons", to improve anything about him that was not flawless. Her lessons for Courage included balancing a heavy set of books on his head while walking up the stairs to "walk perfectly" and to make the Eiffel Tower out of toothpicks so he could "make something perfectly". All of these lessons ended with Courage failing, much to her anger.
However, The Perfectionist eventually met her downfall. When Courage went to the bathroom, he met a friendly Fish, who told him that that there is no such thing as true perfection, and that he could do anything, despite his imperfections. Realizing this, Courage returned to her. The Perfectionist informed Courage that if he fails his "final examination", everywhere he will go he would be known as being "imperfect". Courage's task was to draw a "perfect" six. Courage, in his own creative way drew a paper that folded up into a six. After that, the Teacher melted into the floor in rage, upset at Courage's success, saying what he did was not perfect and vanished into the ground, along with her blackboard shattering into dust-like pieces.
It's possible and speculated that the Teacher melted because the whole time, she was a figment of Courage's mind. When Courage learned to finally accept himself, it destroyed his insecurities.
Not much is known about The Perfectionist, but what is known is that she is a schoolteacher who teaches her students how to be "perfect." This is evidenced by Di Lung's appearance in Perfect, who had built a gigantic Eiffel Tower out of toothpicks, implying that she had taught him how to be "perfect", and that Di Lung apparently continued on with his life being "perfect". Other than that, there is no reference to The Perfectionist's younger days, which might lead to why she believed in perfection and why she taught people how to be flawless.
It is quite possible that she is a manifestation of Courage's own doubts and insecurities that have plagued him the entire series. Although, it is also possible that she is a spirit of sorts who manifests wherever self-doubt and insecurities lay, as Di Lung had also been one of her students before Courage. Regardless, this would explain why only certain people can see her and are aware of her and why later she melts into nothing when Courage learns to finally accept himself.
- On Cartoon Network's online episode viewer in the episode's description, she is named "The Perfectionist". It is unknown if this is her actual name.