Ms. Bitters is a supporting antagonist in the animated series Invader Zim. She is the teacher of Zim's and Dib's class at Skool.
A tall, slender old woman of unknown origin or age, she is a very grouchy teacher, who has devoid of any positive emotion and full of demonic hatred for children. Ms. Bitters is voiced by the late Lucille Bliss who also voiced Anastasia Tremaine. Her first name is unknown.
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, feeding the possibility that she is inhuman. Details on her history is unknown.
Whatever she is, she cannot survive in direct sunlight, as seen in The Voting of the Doomed. In this same episode, she is wearing a black cloak like a vampire, thought to protect her from the sun. She greatly dislikes children, and has expressed frustration at school over-crowding, as well as disdain for traditional holidays such as Halloween and Valentine's Day (although dislike for the latter could be justified, considering an unknown event in the past changed the Valentine's Day tradition from giving out chocolate and cards to giving "Valentine meat slabs"). In the Halloween Spectacular of Spooky Doom, she is revealed to have an even more demonic doppelgänger in an alternate dimension: A gremlin-like creature known as Nightmare Bitters, who is after Dib's head. She tried to get into Dib's true world, but went back after seeing how
Ms. Bitters is very cold, sadistic and behaves more of a corrupt dictator than a classroom teacher. She doesn't really care for her students or their futures whatsoever, she even insults her current students' parents who were her former students for not growing up to be successful or rich. Bitters has no qualms forcing them to use garbage-filled trash cans instead of desks because she refuses to spend any of the school's money on desks, constituting a health hazard for her students. She also forced her students to sell sawdust passed off as candy bars door-to-door and intended to use that money for either her own benefit or the candy company's own benefit and not use that money to buy actual desks for the students. She even imposed ridiculous hall passes on her own students (kicking them out for ludicrous reasons as well) such as a GPS neck bracelet that will explode if outside school perimeters and an iron radiator. She also thoroughly enjoys punishing her students to extreme degrees, such as forcing Dib to clean up Zim's pimple juice that flooded the entire school (which wasn't Dib's fault) with a very tiny sponge instead of a regular-sized kitchen sponge.
- She made a voiceless cameo in Enter the Florpus and doesn't appear anywhere in the story outside of Dib's animesque visualization of how the show progressed (possibly because the story seems to take place during summer). It's likely that Ms. Bitters wasn't brought back due Lucille Bliss' death in 2012.