The Simpsons
Kavner became known for her role as Marge Simpson on the animated television show The Simpsons, a show that continues to the present day. The Tracey Ullman Show included a series of animated shorts about the dysfunctional Simpson family. Voices were needed for the shorts, so the producers decided to ask Kavner and fellow cast member Dan Castellaneta to voice Marge and Homer rather than hire more actors. Kavner has what Hilary de Vries of The New York Times described as a "honeyed gravel voice". Kavner says her voice is due to "a bump on [her] vocal cords".
Although Marge is her highest profile character on the show, Kavner's favorite characters to voice are Marge's sisters Patty and Selma Bouvier because "they're really funny and sad at the same time". Series creator Matt Groening instructed Kavner to voice the duo as characters who "suck the life out of everything". Both have similar raspy voices, but Patty's voice is more masculine and has a lower register, while Selma's voice is a little sweeter. Kavner also provides the voices of every other female member of the Bouvier family, including Marge's mother Jacqueline, Great-Aunt Gladys (a dead relative who was introduced on season four's "Selma's Choice"), and an unnamed grandmother seen on the season six episode "Fear of Flying".
While cast members and crew have referenced Kavner as a deep fan of the series and the characters she voices, part of Kavner's contract says that she will never have to promote The Simpsons on video nor has she performed Marge's voice in public because she believes the publicity "destroys the illusion. People feel these are real people." Kavner takes recording sessions seriously, and feels that voice acting is "a little more limiting than live acting. And I have nothing to do with my character's movement." Nancy Cartwright, who voices Bart Simpson, said in her book My Life as a 10-Year-Old Boy (2000) that Kavner is a warm person who is "a workhorse of an actor" with "extraordinary professionalism and quiet work ethic", and notes that she is rarely late for recording sessions. Kavner had very few recorded interviews in regard to her work on the show. In behind-the-scenes footage from 1992, she describes Marge as "a wonderful person" with "a great sex life". On a 1994 appearance on Late Show with David Letterman, Kavner explains that performing the voice of Marge in a live-action setting would break the illusion of the character, and that she does not want her own likeness to overlap with that of the character. However, after being coaxed by Letterman, Kavner turns to face away from the camera and speaks briefly in the voice of Marge.
Until 1998, Kavner was paid $30,000 per episode. During a pay dispute in 1998, Fox threatened to replace the six main voice actors with new actors, going as far as preparing to cast new voices. However, the dispute was soon resolved and she received $125,000 per episode until 2004 when the voice actors demanded that they be paid $360,000 an episode. The issue was resolved a month later, and Kavner earned $250,000 per episode. Following salary re-negotiations in 2008, the voice actors received approximately $400,000 per episode. Three years later, with Fox threatening to cancel the series unless production costs were cut, Kavner and the other cast members accepted a 30 percent pay cut, down to just over $300,000 per episode.
At the 44th Primetime Emmy Awards, Kavner received a Primetime Emmy Award for Outstanding Voice-Over Performance for voicing Marge in the season three episode "I Married Marge". In 2004, Kavner and Dan Castellaneta won a Young Artist Award for Most Popular Mom & Dad in a TV Series. For her performance in The Simpsons Movie, Kavner was nominated for Best Voice Acting in an Animated Feature at the 2007 Annie Awards, but Ian Holm from Ratatouille received the award. Kavner's emotional performance in the movie got positive reviews, and one critic said she "gave what must be the most heartfelt performance ever to find its way into a movie based on an irreverent cartoon". Some scenes in the movie, such as Marge's emotional video message to Homer, were recorded over 100 times, leaving Kavner exhausted.