Edna Krabappel
Marcia Wallace died on October 25, 2013. The people who worked on the show said that they knew that she was ill. Al Jean (the show's showrunner) was very sad when he learned that Marcia Wallace died. He said that the show will retire her character. This means that she will not usually be in episodes anymore. In "Four Regrettings and a Funeral", the episode's chalkboard gag says "We'll really miss you Mrs. K".