One of the biggest strengths of just how long The Simpsons has been on television is how the series allows initially simple relationships to evolve in organic and heart-wrenching ways, with the bond between Bart Simpson and one of his early "enemies" blossoming into a defining element of the character. The surprisingly empathetic and sweet relationship between Bart and Edna Krabappel is a crucial piece of his development and one of the best bittersweet throughlines within the series.
Krabappel was Bart's fourth grade teacher, introduced early in the show before having the full story of her arrival explained in Season 17, Episode 13, "The Seemingly Never-Ending Story." Krabappel arrived in Springfield to be a teacher and almost left the town before the start of the term -- only to see Bart at school lamenting over his summer detention. Krabappel vowed to become his teacher and guide him towards a better life, unaware that Bart was really there to help Nelson steal computers. It wasn't long before Krabappel's drive for teaching was depleted by a mix of her own loneliness, the lack of support from the school system and the antagonism she received from the student body -- spearheaded by Bart.
However, the pair had a surprisingly sweet relationship grow out of their constant bickering and conflict. In Season 3, Episode 16, "Bart the Lover," one of Bart's pranks resulted in Krabappel falling in love with a non-existent man. Guilty over how this genuinely hurt her, Bart turned to his family for help and crafted a sweet farewell to share with her, allowing her to leave the "relationship" unaware of the prank. Bart was also crucial in helping Krabappel begin a relationship with Seymour Skinner in Season 8, Episode 19, "Grade School Confidential,"ensuring they kept their jobs despite public outcry over their perceived openness with the relationship.
As the series played out, Bart's prankish nature became more focused on Skinner and the school itself, rather than targeting Krabappel. Bart even developed something of a friendship with the teacher, at one point arguing that she's a good enough teacher to survive him and getting her nominated for the Teacher of the Year award in Season 14, Episode 7, "Special Edna."
His cruelest and most dramatic prank against her -- spiking her coffee and briefly costing Krabappel her job in Season 21, Episode 2, "Bart Gets a 'Z'" -- was more of a childish mistake than act of malice, and he helped get her job back. Even at her lowest moments, Krabappel did her best to help Bart grow, taking pity on him at times, such as in Season 2, Episode 1, "Bart Gets an 'F'," where she allowed him to pass the fourth grade for his efforts.
Bart and Krabappel's relationship was a crucial element of Bart's life, with Bart unaware of just how important she was to him until after her death off-screen in Season 25, which was written in respect to the passing of her actress, Marcia Wallace. In Season 32, Episode 12, "The Diary Queen," Bart's self-doubt is reduced after he discovers Krabappel's diary and mistakes her comments about a recently adopted cat as inspirational thoughts about him. Upon learning the truth, Bart is more shaken than ever before, noting to Marge that even an attempt to help him might just push him over the edge. It's only after speaking with her widower, Ned Flanders, that Bart learns she did believe in him, and that faith kept the Flanders from leaving Springfield, as she couldn't depart until she knew Bart would be okay.
Krabappel's impact on Bart has always been one of the most dramatic elements of the latter's character, with his crueler side failing to hold up against the empathy he felt for an often underappreciated woman. Their dynamic proves that no matter how bad he can be, Bart is a good person at heart. This became a central point for the character, keeping him from ever crossing over too much into unlikability or cruelty. At times enemies but never actually hating each other, Bart and Krabappel's bond is one of the most endearing elements of The Simpsons.
The Simpsons stars the voices of Dan Castellaneta, Nancy Cartwright, Harry Shearer, Julie Kavner, Yeardley Smith and Hank Azaria. New episodes air Sundays at 8 p.m. ET/PT on Fox.