Ms. Bitters is a character from the animated Nickelodeon cartoon Invader ZIM. She is the teacher of Zim and Dib's school class. Devoid of any compassionate emotion, she is a tall, slender aged woman of unknown origin. Ms. Bitters is voiced by Lucille Bliss.
Directly pulled from Vasquez's earlier comic book series Squee! (where she was Todd's teacher), she apparently possesses eerie powers, including the ability to materialize out of shadows, float through the air, and adopt snake-like features. The biography on the back of the Nickelodeon electronic trading card (written by Eric Trueheart) states that she has always been where she is, and the "Skool" was built around her.
In some early episodes, she appears to be covered in cockroaches. When her students displease her, she habitually looms over them menacingly with clawed hands and bared teeth.It appears that Ms. Bitters is not human, in the episode Lice, she and Zim were the only ones not affected by lice. However, her actual identity and form is unknown. Whatever she is, she cannot stand sunlight, as seen in The Voting of the Doomed. She dislikes the smell of children, and has expressed frustration at school over-crowding, as well as disdain for traditional holidays such as Halloween and Valentine's Day. Aparently, she likes the Countess von Verminstrasser, as she said in the episode Lice "What a nice lady" when the Countess yelled Dib for not taking the lice problem too seriously. Strangely, the Countess looks a little to Mrs. Bitters, but maybe it can be a coincidence. http://badbadrubberpiggy.com/images/caps/iz12/large/iz12-00135.jpg
She sometimes horrifies her students with grotesque recollections: she claims to have once been a fairy princess until she was shocked with a bugzapper in Halloween Spectacular of Spooky Doom, which she claims "One day it all went horribly wrong!", and in Career Day she claims to have been an astronaut whose spaceship imploded. She said this was a lesson that dreams lead to fatal implosions. It is revealed in the DVD commentaries that many more Ms. Bitters flashbacks were to occur in the series, but they constantly had to be cut due to time constraints. She also has a deranged (and darkly humorous) disposition, which she uses as "lessons", such as "The unvierse, and how it will eventually implode in on itself" and "Our whole society is nothing more than a perilous house of cards, destined to collapse under its own weight". Ms. Bitters favorite student appears to be Zita. Her least favorite student appears to be Dib. Zim has also shown a degree of fear towards her as once when given orders by her he follows them in a mechanical fashion. Oddly Mrs Bitters appears to be one of the very few humans that Zim does not openly hate, proclaim his superiority over or act violently towards. Indeed, Zim seems to be completely neutral to Mrs Bitters even when she threatens him or is cruel, he even salutes her in one episode("Room with a Moose") and unlike some other students rarely questions anything she does.