Last week, actress Marcia Wallace died at age 70 due to complications from pneumonia, after a long career that included more than two decades spent voicing Bart Simpson's weary fourth-grade teacher, Mrs. Edna Krabappel. As originally written, Mrs. Krabappel could have been a one-note character — but Wallace's stellar performance saw her evolve into one of The Simpsons' most reliable and poignant guest characters, as she juggled an unsatisfying love life and sparred with her sometimes adversary, sometimes ally Bart.

It's unclear how the show will account for her absence, though producer Al Jean told Entertainment Weekly that the character will be retired. But whatever the future of the series, there are nearly 200 episodes that feature Wallace's unmistakable performance for fans to consume. Here, six of the best Simpsons episodes featuring Edna Krabappel:

1. "Bart Gets an F"

It might sound ridiculous to modern viewers weaned on shows like South Park and Family Guy, but there was a time when The Simpsons' lightweight antics were the most controversial thing on television — and much of the chatter centered on Bart, who was widely attacked in some quarters as a poor role model for children.

Episodes like "Bart Gets an F," which opened the show's second season on Fox, shows how misplaced that criticism really was. When Mrs. Krabappel tells Bart that his perennial slacking means that he might need to repeat the fourth grade, he desperately studies for a last-chance test — and earns a grade that's a single point below the D- he needs to pass.

"Bart Gets an F" works, in large part, due to Marcia Wallace's measured performance as Edna Krabappel. Wallace displayed an amazing range of emotions in a single episode, breathing life into the character as she shifts from irritation to compassion as she realizes how hard Bart has studied, and awards him the final point he needs. The episode showed how much potential there was in the surprisingly textured relationship between Bart and Mrs. Krabappel, which went on to serve as the center for some of The Simpsons' greatest episodes.

2. "Bart the Lover"

If "Bart Gets an F" demonstrated the potential of exploring Bart and Mrs. Krabappel's adversarial relationship, "Bart the Lover" showed just how poignant Mrs. Krabappel could be. The episode is a heartbreaking, beautifully realized portrait of middle-aged ennui, as Mrs. Krabappel places a personal ad in the "lonely singles" section of the local newspaper. When Bart discovers the ad, he invents "Woodrow," a hyper-idealized mate, and uses him to trick Mrs. Krabappel into thinking she's finally found true love. When she's inevitably stood up by her fictional suitor, Bart realizes the damage he's caused, and enlists the help of his family to craft a final letter that lets Mrs. Krabappel down easy without breaking her heart any further. Wallace's achingly soulful performance earned her an Emmy for Outstanding Voiceover Performance, which makes her one of just three guest performers in The Simpsons' history to do so.

3. "Lisa's Substitute"

Mrs. Krabappel's character arc was complex and sometimes tragic, but she was also one of the show's funniest supporting characters. "Lisa's Substitute" is focused almost entirely on the relationship between Lisa and a supportive substitute teacher voiced by guest star Dustin Hoffman, but Wallace almost runs away with the episode by delivering a dead-on parody of The Graduate's famous "Mrs. Robinson, you're trying to seduce me" scene.

4. "Grade School Confidential"

Mrs. Krabappel's love life was at the center of yet another strong episode, when Mrs. Krabappel and Principal Skinner realize they're into each other. After Bart catches them making out in the school's broom closet, word eventually spreads across town, and they're forced to defend their relationship or risk losing their careers. The episode kicked off a long-running, on/off relationship between the two characters.

5. "Special Edna"

Mrs. Krabappel and Principal Skinner's tumultuous relationship came to a head in "Special Edna," which saw Bart consoling his teacher after Skinner stood her up due to the intervention of his controlling mother. When Bart nominates her for teacher of the year, Skinner becomes afraid that she'll leave both him and the school itself — and though she doesn't win the award, she does accept a marriage proposal from Skinner. Alas, the wedding wasn't to be; in the following year's "My Big Fat Geek Wedding," the couple called it off just days before they were scheduled for the altar.

6. "The Ned-Liest Catch"

Skinner didn't turn out to be her true love, but Mrs. Krabappel did end up in a happily wedded relationship — and it was all thanks to Simpsons fans. Season 22's "The Ned-Liest Catch" saw the beginning of a relationship between Mrs. Krabappel and the widowed Ned Flanders, and invited fans to vote on whether or not the relationship would work out. After a poll on that executive producer Al Jean said was "very strong in one direction," season 23's "The Falcon and the D'ohman" revealed that the couple had stayed together — giving Edna Krabappel the happy, stable relationship she'd craved since the beginning of the series.