Marcia Wallace, the voice of Mrs. Krabappel, died of pneumonia complications Friday night at the age of 70.

Once a student teacher in Iowa, Wallace moved to New York in 1964 and got her start in show business typing scripts. She eventually worked her way up to regular appearances on The Merv Griffin Show, which caught the attention of CBS founder Bill Paley, who personally demanded she be given a role on The Bob Newhart Show in 1972. For six seasons (and a 1994 episode of Murphy Brown), Wallace played the smart-mouthed and lovelorn secretary Carol Kester, a role that made her a star. Afterwards, she became a regular on various game shows, including Hollywood Squares. In the late 1980s she became a voice actress for cartoons including Darkwing Duck, Captain Planet, and The Simpsons. She was also a stage actress in a number of regional productions, including a starring role in An Almost Perfect Person.

Diagnosed with breast cancer in 1985, Wallace became an activist for breast cancer awareness and a motivational speaker. She lost her husband of six years, Dennis Hawley, to pancreatic cancer in 1992, leaving her to raise their adopted son alone. She wrote about her ordeals in her 2004 memoir, Don’t Look Back, We’re Not Going That Way:

Ten years ago, I was a devastated widow with a little kid, a house that was ready to be foreclosed, and a hundred thousand dollars’ worth of debts. Now all that’s paid off and my house is secure. And I’m opening up to new possibilities. Who knows what’s around the corner? I feel ready to find out. You know me, hon, I’m a scrappy gal. And I’m not looking back… ’cause I’m not going that way.

For 25 seasons, Marcia Wallace played Edna Krabappel, Bart Simpson’s acerbic chain-smoking fourth grade teacher. Openly disdainful of her students, Krabappel was a exquisite personification of an uncaring public school system, and her caustic “ha!” became a trademark. She dated Principal Skinner a while, and in recent seasons married Ned Flanders. Wallace won an Emmy in 1992 for her performance in the episode “Bart the Lover.”

Technically a recurring guest star, Wallace is the third cast member of the The Simpsons to pass away, following Doris Grau (Lunchlady Doris) in 1995 and Phil Hartman (Lionel Hutz, Troy McClure) in 1998. As with Hartman’s characters, Mrs. Krabappel’s “irreplaceable character” will be retired, according to showrunner Al Jean:

Before her death Wallace “recorded several lines which will appear in upcoming shows,” Jean said. “But I don’t intend to have anyone else play Mrs. Krabappel. I think Bart will get a new teacher and Ned Flanders will be a widower again.”

Simpsons staffers have been expressing their sympathies. Jean told the Los Angeles Times that she was “sweet, funny, not at all pretentious […] and just a wonderful person to be around.” Co-star Yeardley Smith tweeted “Heaven is now a much funnier place b/c of you, Marcia.” Director David Silverman drew a tribute sketch.

Wallace has a small role in the upcoming film Muffin Top: A Love Story, scheduled for release next year.

[Deadline, TMZ, MarciaWallace.com, Entertainment Weekly, Los Angeles Times]