(CNN) -- Marcia Wallace, whose four-decade television career included playing the receptionist on "The Bob Newhart Show" and Bart's fourth-grade teacher on "The Simpsons," has died, her agent said Saturday.
Wallace was 70, according to imdb.com. Her cause of death was not immediately confirmed.
Wallace starred for six seasons as Carol Kester on "The Bob Newhart Show" in the 1970s and reprised the role in the 1990s on "Murphy Brown."
But it was her Emmy-winning role as Edna Krabappel, Bart Simpson's teacher with the snarky laugh, that may have earned her the most fame in recent years. It was a part she held since the show's premiere in 1990.
"I was tremendously saddened to learn this morning of the passing of the brilliant and gracious Marcia Wallace," executive producer Al Jean of "The Simpsons" said in a statement. "She was beloved by all at 'The Simpsons' and we intend to retire her irreplaceable character."
Jean said rumors that the show had already planned to retire Wallace's character are not true, he added.
"Marcia's passing is unrelated and again, a terrible loss for all who had the pleasure of knowing her," Jean said.
Wallace was a regular guest star on a host of popular TV shows in the 1970s and 1980s, from "The Love Boat" and "Fantasy Island" to "Gimme a Break!", "ALF," "Night Court," "Charles in Charge" and "Magnum, P.I."
She was also a mainstay of TV game shows such "The Hollywood Squares," "Password" and "The (New) $25,000 Pyramid" and starred in numerous stage productions, including a touring production of "The Vagina Monologues."
In recent years, Wallace also advocated for awareness of breast cancer, a disease she battled herself. Her 2004 book, "Don't Look Back, We're Not Going That Way," in part chronicled her fight.
CNN's David Daniel and Henry Hanks contributed to this report.