Ms. Bitters is the teacher of Zim's and Dib's class at Skool. A tall, slender old woman of unknown origin or age, she is devoid of any positive emotion, and full of demonic hatred for children. She evidently possesses paranormal powers, including the ability to materialize out of shadows, levitate, and adopt snake-like, and, occasionally, spider-like movement as it was discovered that she is not human, and that she did not come to work at the Skool, but rather, was always there, 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, feeding the possibility that she is inhuman. Details on her history is unknown. Whatever she is, she cannot survive in direct sunlight, and shows disdain for traditional holidays such as Halloween and Valentine's Day. She often horrifies her students with grotesque "recollections": like she claims to have once been a fairy princess until she was shocked with a bug zapper, and she claims to have been an astronaut whose spaceship imploded. She also has a dark disposition, which she puts to good use in her "lessons". One of said "lessons" was to memorize the copyright information of one of the textbooks, and she stated there would be a quiz on it.