Perfectionist

The Perfectionist as she proclaims herself in that profession, is a villain that appears in "Perfect". She is an elderly schoolteacher under the alias "The Teacher", who helps people be "perfect" through the use of lessons to help them achieve the status of being perfect. Courage was going through a day of not doing things right, so The Teacher came to the farmhouse (with Muriel and Eustace unaware of her presence) to strictly train Courage into becoming "perfect".

The Teacher had Courage enroll in various "perfection lessons", to improve anything about him that was not flawless. Such lessons were things such as Courage having to balance a heavy set of books on his head while going up the stairs to "walk perfectly", and to make the Eiffel Tower out of toothpicks so he could prove he could "make something perfectly". All of these lessons ended with Courage failing the task, much to the anger of The Teacher.

However, The Teacher 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. Realising this, Courage returned to The Teacher. The schoolteacher informed the dog 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. He drew an odd picture and folded the paper and turned it upside down. The Teacher found a six on the paper. She then melted into the ground 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 dustlike pieces.

Background
Not much is known about The Teacher, 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 Teacher's younger days, which probably might lead to why she believes in perfection and why she teaches people how to be flawless.